73+ 
 
 
 
 
AGRIC. LIBRARY 
 
 LIBRARY 
 
 UNIVERSITY OF CALIFORNIA. 
 
 GIF-T OF 
 
 r\ 
 Class 
 
BACTERIA 
 
 IN THEIR 
 
 BELATION TO VEGETABLE TISSUE 
 
 A DISSERTATION 
 
 PRESENTED TO THE BOARD OF UNIVERSITY STUDIES OF THE 
 
 JOHNS HOPKINS UNIVERSITY FOR THE DEGREE 
 
 OF DOCTOR OF PHILOSOPHY 
 
 BY 
 
 H. L. RUSSELL 
 
 *7 
 
 1892 
 
 PRESS OP 
 
 THE FRIEDENWALD COMPANY 
 BALTIMORE 
 

 
 
CONTENTS. 
 
 PAGE 
 
 Introduction 1 
 
 Current views as to the exemption of vegetable tissue from attacks of micro- 
 organisms 2 
 
 Methods used in experimental work 3 
 
 Do healthy plant tissues normally contain bacteria ? 4 
 
 Results of artificial inoculation of bacteria into vegetable tissues : 
 
 1. With saprophytic species 5 
 
 2. With species parasitic for animals 6 
 
 3. With species parasitic for plants . 7 
 
 Conclusions derived and arguments to show that distribution of germs in tissue 
 
 depends upon actual growth 8 
 
 Can bacteria penetrate the intact healthy membranes of the plant ? 11 
 
 The action of bacteria within the tissues, their mode of transport, etc 13 
 
 Resistance and immunity of plants toward bacteria 15 
 
 Distinction between normal resistance and immunity in the plant organism . . 17 
 
 Examples illustrating the phenomena of resistance and immunity 20 
 
 Causes producing this condition 23 
 
 Physical 24 
 
 Chemical 26 
 
 Do plant juices possess germicidal properties ? 27 
 
 Conclusions 32 
 
 Bibliography 34 
 
 Appendix giving a tabular resume of all the bacterial plant diseases known to 
 
 date . . 35 
 

 BACTERIA IN THEIR RELATION TO VEGETABLE 
 
 TISSUE. 
 
 BY H. L. RUSSELL. 
 
 The relations of that group of micro-organisms known as bacteria 
 to the animal kingdom have within the past two decades been made 
 the subject of unusual attention. 
 
 No department of the rapidly developing branches of science has 
 been the field of greater activity, yet, strange to say, the relations 
 which these organisms bear to the co-ordinate branch of biology, the 
 vegetable kingdom, have been greatly neglected. 
 
 Botanists have studied bacteria as a class, more or less, in order to 
 determine, if possible, their affinities with other low forms of life, but 
 the greater activity in this field has been largely due to the close 
 relation which they bear to medicine in the etiology of disease. 
 
 In regard to the relations which they bear to and the influence that 
 they exert upon higher plant life, the data we possess are meager. 
 The progress which has already been made in this department of 
 plant pathology comes largely from this side of the Atlantic, and to a 
 prominent American botanist, Prof. T. J. Burrill, belongs the honor 
 of having been the first to work out the causal relation between a 
 specific microbe and, a plant malady (pear-blight, 1878). 
 
 Although Prof. BurrilPs work was done over a decade ago, com- 
 paratively little notice has been taken of it by European writers, 
 with but few exceptions, and the majority of the text-books that refer 
 to it at all regard the case as not thoroughly proven ; but upon what 
 grounds these conclusions are based it is quite impossible for one to 
 understand who has had access to the already widely published data. 
 
 It seems to be a wide-spread belief that plants do not suffer to any 
 great extent from the attacks of these micro-organisms. The reasons 
 usually assigned for this so-called immunity are various. Chief 
 among them, however, is that which bases the freedom of plants from 
 bacterial attack upon the acidity of the plant-tissue. Other subsidi- 
 ary reasons are also advanced by various authors. 
 
2 H. L. Russdl 
 
 Fliigge 1 states that bacteria almost never attack higher plants, 
 giving as an only exception Wakker's hyacinth-disease. The low 
 temperature of plants and the chemical composition of vegetable 
 juices he regards as very unfavorable for the development of bacteria, 
 more especially as the cell-juices almost always possess a distinct 
 acid reaction, and thus protect the plant against these micro- 
 organisms, which are so sensitive in this respect. 
 
 Hartig,in the recent edition of his Lehrbuch der Baumkrankheiten 
 (p. 37), also urges the view that the acid reaction of plants prevents 
 the growth and development of bacteria, and that they play a very 
 unimportant role in the production of plant-disease. In the hyacinth- 
 disease above referred to, he says the bacteria do not attack sound, 
 well-ripened bulbs under normal conditions,but only when the tissues 
 have been more or less injured by wounds or previous attacks of fungi. 
 
 He notices, also, BurrilPs claim that the pear-blight is caused by 
 a specific bacillus, but is somewhat skeptical that the form referred 
 to is anything but a secondary accompaniment of the malady. 
 
 DeBary is inclined to support the general views advanced by 
 Hartig, but in his last edition of Die Bakterien (S. 36) he states that 
 it might be possible for bacteria to gain access, through stomata, into 
 the tissues of higher plants, but that this is probable is yet undeter- 
 mined and needs further investigation. 
 
 These observers, all of them recognized authorities in the realm of 
 pathology, seem to regard it as quite improbable that bacteria have 
 any important bearing upon the production of plant-disease. Whether 
 this unanimity of expression is due to the actual absence of bacterial 
 plant-maladies in Europe generally, or because investigations have 
 not been directed in these channels, can only be inferred. 
 
 In consideration of the fact that this branch of vegetable pathology 
 is of increasing importance, and that the reasons assigned for the 
 apparent exemption of plant-tissues from the attacks of micro-organ- 
 isms have been largely based upon the general law known in regard 
 to bacterial life in general, it was deemed advisable that a series of 
 investigations should be carried out with different micro-organisms, 
 to see what effect contact with the living plant-tissues would have 
 upon them; so, at the suggestion of Prof. Welch, this topic was taken 
 up for consideration. 
 
 1 Die Mikroorganismen, S. 515. 
 
Bacteria in their Relation to Vegetable Tissue. 3 
 
 I have been unable to find any literature upon this particular 
 question with the exception of a preliminary report by Lominsky, 
 who worked mainly with those forms which are pathogenic for 
 animals. His original paper is in Russian, so I have been forced to 
 rely solely upon an abstract (Cent, fur Bakt., Bd. VIII, 325) for 
 his data. 
 
 Aside from this single exception, I find no general series of 
 experiments recorded as giving the effect of vegetable tissues upon 
 various forms of bacterial life. 
 
 METHOD OF EXPERIMENT. 
 
 The following outline will indicate the manner in which the 
 experiments were carried out. Fresh cultures of the various micro- 
 organisms were always taken (usually bouillon cultures 12-24 hrs. 
 old), so as to insure the introduction of non-sporogenous material. 
 A young growing stem was selected, so as to give the most favorable 
 conditions for the, development of the organism. It was first washed 
 with sterile water and then pierced with a fine sterilized platinum 
 needle. Into this minute opening a tiny droplet of culture fluid was 
 injected from a capillary pipette. The slight puncture caused by 
 the penetration of the needle was then closed from the influence of 
 air and possibility of accidental contamination, by sterile vaseline. 
 
 The results were determined by excising a section of the infected 
 stem, the surface having been slightly flamed in a Bunsen flame. 
 
 The cortical layer was then removed with a sterile scalpel, leaving 
 the inner tissue into which the organism had been injected. Quite 
 thin sections of this remaining tissue were cut, under aseptic precau- 
 tions, and inoculated into tubes of melted gelatine and roll cultures 
 made therefrom. As the fluid gelatine easily penetrates the plant- 
 tissue, a moderately thin section may be examined, under considerable 
 magnification, with ease. The tissue was sectioned, not only at the 
 inoculation point, but at varying distances above and below. By 
 growing these serial sections in sets of culture tubes, one is able to 
 determine how far the bacteria have spread .throughout the plant. 
 
 An objection to this method lies in the fact that small variations 
 in the germ-content cannot be detected, as it is quite impossible to 
 prepare the tissue so that all germs present can develop ; but where 
 cultures made from tissue taken at the point of inoculation reveal 
 
4 H. L. Russell. 
 
 but few germs, we may safely conclude that they have either been 
 killed off by the plant or died from insufficient nutrition. 
 
 On the other hand, an increase can only be considered probable 
 where the cultures, not only from tne tissue immediately surrounding 
 the inoculation point, but at a distance from it, reveal a large number 
 of germs. Even the fact that bacteria are to be found at a greater or 
 less distance from point of introduction does not necessarily show 
 that an actual increase has taken place. Their presence at this point 
 might be considered as due either to simple diffusion or to mechani- 
 cal transportation by the fluids of the plant. The effect of these 
 possible factors will, however, be shown later to be quite nugatory. 
 
 If macroscopical changes are to be seen in the tissue, it would be 
 of itself sufficient evidence that actual multiplication of the micro- 
 organisms had taken place. In addition to culture methods to deter- 
 mine the presence or absence of bacteria in the infected tissues, sec- 
 tions were also subjected to microscopical examination. 
 
 But this method proved quite unsatisfactory, except where the 
 bacteria in the tissues were numerous, as in the case of actual infec- 
 tion. The granular detritus and peculiar rod-like masses of proto- 
 plasm often found in matured cells make it extremely difficult to 
 differentiate the bacteria in an unstained condition. The use of 
 staining methods, so successful in the differentiation of bacteria in 
 sections of animal tissue, have not as yet been successfully applied to 
 bacteria in plants. The aniline stains, toward which the bacteria 
 are so susceptible, seem to impregnate the vegetable cell and its 
 membranes with great ease, and in the use of decolorizing agents, 
 parts of the plant cell retain the stain as deeply as do the bacteria. 
 
 Before detailing the results of the experiments made, we will con- 
 sider briefly the presence of bacteria in normal uninjured plant- 
 tissues. This, for a considerable time, has been a debatable question, 
 and the recorded results of numerous observers are somewhat at 
 variance with one another. 1 The preponderance of evidence is, how- 
 ever, certainly against the view that micro-organisms are present 
 normally in the tissues of higher plants, and this conclusion harmon- 
 izes well with what we know in the domain of animal life. 
 
 In the examination of plant-tissues I have made a large number 
 of cultures, according to the method described above, from plants 
 
 1 See bibliography, page 34. 
 
Bacteria in their Relation to Vegetable Tissue. 
 
 selected as healthy in all respects, without being able to isolate bac- 
 teria from them. Bacteria, however, were often found in tissue which 
 had been wounded from any cause, and in some cases in such num- 
 bers as to lead one to think that they had possibly multiplied in the 
 plant-tissue. This can happen from the local death of the wounded 
 tissue, which will enable the micro-organisms to gain a foothold, and 
 even though they may not be able to grow within the living plant, 
 they are able to exist for a considerable length of time (as will be shown 
 by the results of artificial inoculation), and thus come to be enclosed 
 in the plant by the healing over of the wounded tissue. This is, I 
 think, a probable explanation of the data recorded by some observers 
 who claim to have actually isolated saprophytic forms from plant- 
 tissues. 1 Lesions so slight as to escape notice, especially in root 
 crops, would allow the access of saprophytic forms to the tissues of the 
 plant, where they might survive for a considerable length of time. 
 
 From the results of my own experiments, the conclusion seems 
 evident that, normally, the healthy plant, with intact outer membranes, 
 is free from bacteria within its tissues. 
 
 In the tabulated results obtained by the artificial inoculation of 
 different bacterial species into vegetable tissue, they will be classified 
 according to their nutritive adaptation. 
 
 TABLE SHOWING ACTION OF SAPROPHYTES IN PLANT TISSUE. 
 
 Name of Germ. 
 
 Date of In- 
 oculation. 
 
 Date of 
 Close of 
 Exp. 
 
 Period of 
 Incuba- 
 tion. 
 Days. 
 
 Host Plant. 
 
 Result. 
 
 B. prodigiosus 
 
 X. 20 
 
 XI. 17 
 
 27 
 
 Tradescantia 
 
 #*2 *" 
 
 
 
 
 
 X. 20 
 XL 26 
 XII. 20 
 XII. 20 
 
 II. 1 
 XII. 5 
 II. 2 
 II. 2 
 
 103 
 10 
 42 
 48 
 
 < 
 
 Geranium. 
 
 
 
 
 
 * 
 ft* 
 
 ** 
 
 B lllt6US .... 
 
 XI. 28 
 XII 20 
 
 XII. 10 
 
 I 28 
 
 13 
 
 40 
 
 Lima Bean. 
 Geranium 
 
 * 
 ** 
 
 B megaterium . . 
 
 XI 19 
 
 XI 30 
 
 11 
 
 Lima Bean 
 
 * 
 
 
 B coli commune 
 
 XI. 19 
 1.12 
 XII 1 
 
 XI. 30 
 11.25 
 XII 20 
 
 11 
 44 
 19 
 
 it 
 
 Geranium. 
 
 jt 
 ** 
 
 ' < 
 
 XII. 1 
 I 12 
 
 XII. 30 
 II 16 
 
 29 
 35 
 
 
 ## 
 
 * 
 
 
 1. 12 
 
 II 24 
 
 43 
 
 
 ** 
 
 B Icictis aerogenes 
 
 I 4 
 
 U14 
 
 '10 
 
 
 
 
 
 
 
 
 
 
 1 Fazio and others : Revista Internaz. d'Igiene, (1890), I, 3. 
 
 2 Explanation of signs : * denotes presence in moderate numbers. 
 
 ** " " " large " 
 
 " absence in culture entirely. 
 
6 H. L. Russell. 
 
 The above table indicates that a number of different forms which 
 are ordinarily saprophytic in their method of nutrition, are able to 
 exist within the plant for a considerable period of time, and in some 
 cases show evidence of a considerable increase. This multiplication 
 does not, however, reach a stage macroscopically observable. There 
 is usually a slight "browning" or discoloration of the tissue at the 
 seat of inoculation, but this is due to the slight injury caused by the 
 inoculating needle, even though the opening is protected from the 
 influence of the air by vaseline. 
 
 The results which were obtained by Lominsky 1 in regard to the 
 growth of Bac. prodigiosus I was unable to confirm. He states that 
 this germ, inoculated into the leaves of certain plants, produced 
 brick-red spots and stripes which were to be seen by the naked eye. 
 In the above experiment bacteria were demonstrated as present in 
 large numbers in tissue even after a considerable lapse of time, 
 but no signs could be detected of a change in the cellular structure 
 in any case. 
 
 In regard to forms which are naturally pathogenic for animals, we 
 might expect a priori that they would be unable to survive for such 
 a length of time, or show as marked an increase, as saprophytic forms, 
 which are, as a rule, less sensitive in regard to the substratum for 
 their development. This expectation was realized, as will be seen 
 from the subjoined table, which comprises those forms that are 
 natural facultative parasites on animals. 
 
 In this group of parasites I find, with but few exceptions, that 
 they are unable to compete with the unfavorable environment to 
 which they are subjected in the plant. The large majority of them 
 are not able even to hold their own, but gradually succumb to their 
 unfavorable surroundings. Here again I failed to verify some of 
 the results obtained by Lominsky. His experiments were confined 
 to the action of plant-tissues upon anthrax, the typhoid bacillus, and 
 Staph. pyog. aureus. He made quite a number of experiments, and 
 found that both the anthrax and the pyogenic organism increased and 
 were able to form colonies in the tissues. Anthrax grew rapidly 
 for a time, formed spores, and finally seemed to undergo degen- 
 eration. The typhoid-fever bacillus was unable, however, to live 
 beyond a few days, and even then showed degenerating peculiarities. 
 
 1 Loc. cit. 
 
Bacteria in their Relation to Vegetable Tissue. 
 
 \*A>. /t : ->ow\x 
 
 TABLE SHOWING ACTION OF ANIMAL PABASITIC FORMS IN 
 VEGETABLE TISSUE. 
 
 Name of Germ. 
 
 Date of In- 
 oculation. 
 
 End of 
 Experi- 
 ment. 
 
 Period of 
 Incuba- 
 tion. 
 Days. 
 
 Host Plant. 
 
 Result. 
 
 B pyocyaneus 
 
 XL 27 
 
 II. 4 
 
 69 
 
 Begonia, cult 
 
 ** 
 
 
 
 c t 
 
 B. anthracis 
 
 XL 28 
 XL 27 
 XL 20 
 
 XII. 30 
 I. 2 
 I. 26 
 
 32 
 36 
 
 38 
 
 Geranium. 
 Penthorum. 
 Geranium. 
 
 ** *-<^ 
 
 -X-* 
 
 < * 
 Staph. epid. alb 
 
 XL 19 
 XL 20 
 XI 20 
 
 XL 30 
 XL 25 
 
 I. 28 
 
 11 
 5 
 40 
 
 Lima Bean. 
 Echino cactus. 
 Geranium. 
 
 (6) 1 
 (2) 
 
 Staph. pyog. aureus. 
 
 a, (( 
 
 Mic C6reus flav 
 
 I. 12 
 XII. 10 
 I 12 
 
 11.23 
 XII. 23 
 II 19 
 
 42 
 13 
 
 38 
 
 ft 
 
 Lima Bean. 
 Geranium 
 
 (3) 
 (4) 
 
 Cholera gallinarum. . 
 Schweineseuche 
 
 II. 20 
 III 8 
 
 III. 10 
 III 25 
 
 18 
 17 
 
 (i 
 
 y' 
 
 ** 
 
 Mic tetragenus 
 
 III 22 
 
 IV 16 
 
 25 
 
 
 
 
 Bac diphtherisB 
 
 III 8 
 
 III 18 
 
 10 
 
 14 
 
 
 
 
 
 
 
 
 1 Numbers in parenthesis indicate number of colonies found in culture made from 
 infected tissue. 
 
 It is noteworthy in the above table that the pyogenic organisms 
 in general do not seem to be especially resistant. With the single 
 exception of the blue pus-germ, they succumbed to the unfavorable 
 influence of the plant-tissues. 
 
 The consideration of the third class, that of bacterial plant para- 
 sites, brings us to those forms which are, in a restricted sense at least, 
 the natural enemies, of vegetable life. 
 
 I have found it impossible to obtain cultures of more than a few 
 of the germs which have been reported as having been isolated in the 
 various plant-maladies, as in many cases cultures are not kept in 
 stock, even by the discoverers of the germ. 
 
 Of those secured I made a series of infection experiments in a 
 number of different hosts, to ascertain the effect of vegetable tissues 
 in other than their natural hosts. 
 
 The pear-blight germ grown in a Begonia-plant for 30 days showed 
 at end of that time large numbers at inoculation point, but not dis- 
 tributed throughout the plant. The same result was found when 
 injected into Phaseolus vulgar is for 30 days, also in Ph. lunatus for 
 16 days. In Tradescantia alba, no trace could be found at the end 
 of 60 days' incubation in this tissue. Bac. avense was injected into 
 tissue of Begonia, onion, corn, wheat, and squash, but in no case 
 
H. L. Russell. 
 
 was any pathological change macroscopically observable. The 
 bacilli were not killed out in the plant-tissue, however, as they were 
 isolated from Begonia and squash in large numbers, after 30 days 7 
 incubation in these tissues, but their presence was confined to the 
 tissue contiguous to point of introduction. 
 
 The results of the foregoing inoculation experiments made with 
 various forms of micro-organisms, saprophytes as well as parasites 
 (both for animals and vegetables), show that these germs in many 
 cases are able to live in the plant-tissues for a considerable length of 
 time. A number of the different forms, particularly saprophytes, 
 are able to grow and spread throughout the plant to a limited 
 extent. Of the parasitic species tested, very few showed any ten- 
 dency to thus spread. Even those forms that are natural parasites 
 of certain higher vegetable species showed no power to spread in 
 plants which were not their natural hosts, but they were able to live 
 at inoculation-point for a considerable time. 
 
 The possible objection, already alluded to, that the distribution of 
 the bacteria, which was noted in many cases, may not indicate actual 
 growth, will now be considered. 
 
 The observed facts are these: The distribution of the micro- 
 organisms in the plant-axis, as determined by culture experiments, 
 always took place in an ascending direction. This distance varied 
 from 30-50 mm. from point of introduction, but in no case were bac- 
 teria found more than 2-3 mm. below inoculation-point. 
 
 Germ. 
 
 Culture from Inoc. 
 Point showed : 
 
 Culture made from 
 Tissue taken. 
 
 Bac. luteus in Geranium 40 days. 
 
 
 1850 colonies, 
 
 10 mm. above, 1764 
 
 B. fluorescens 
 
 43 
 
 
 
 4200 
 
 
 5 
 
 3850 
 
 
 
 <i 
 
 
 
 
 
 
 3 
 
 below, 350 
 
 B. butvricus 
 
 48 
 
 
 
 104 
 
 
 5 
 
 above, 45 
 
 " 
 
 
 
 
 
 
 
 
 10 
 
 20 
 
 B. acidi lactici 
 
 35 
 
 
 
 6500 
 
 
 5 
 
 4200 
 
 
 
 
 
 
 
 
 
 
 25 
 
 2250 
 
 
 
 
 
 
 
 
 
 
 3 
 
 below, 2000 
 
 Of course the numbers given above do not represent the total 
 number of bacteria present, owing to the difficulty of preparing tissue 
 so that all can develop. Besides this fact, the developing colonies 
 were observed to be usually intracellular and not in the spaces of the 
 plant. 
 
Bacteria in their Relation to Vegetable Tissue. 9 
 
 Now let us consider the two possible theories, besides that of actual 
 growth, which suggest themselves. 
 
 First, that of diffusion. For this a fluid substance is necessary 
 that is continuous throughout the plant. As the cellulose wall and 
 ectoplasm of the vegetable cell act as an effectual filter of solid 
 particles, there would be no chance for direct diffusion from cell 
 to cell. The inability to utilize the intercellular spaces for this 
 purpose is equally evident, for these are, under normal conditions, 
 filled only with a saturated vapor, and not fluid substances, and there- 
 fore unable to function as a means of diffusion. 
 
 If simple diffusion were operative, then, too, we would expect to 
 find the bacteria diffused as far below the point of introduction as 
 above, especially as gravity would aid in this result. This is con- 
 trary to the experimental facts. 
 
 Now, is it possible to explain this distribution as a result of the 
 transpiration currents in the stem? 
 
 Whatever may be the ultimate outcome of the conflicting theories 
 regarding the locus of the transpiration stream, it rests upon the 
 imbibitory and osmotic powers of certain vegetable cells. But this 
 stream can only carry substances in solution through these vegeta- 
 ble membranes, and therefore could not function as a transporter of 
 solid bodies like bacteria. This was demonstrated by cutting the 
 stem of a thrifty growing plant under water, and then transferring it to 
 a vessel containing a nutrient solution to which a dilute culture of a 
 germ had been added. It was found that in the exercise of the ordi- 
 nary processes of vegetation, no germs were detected in the tissue to 
 any considerable distance above the water level. 1 
 
 Then, too, the distribution of the bacteria in different tissues, such 
 as the cortical and pith parenchyma, as well as the fibro-vascular 
 tissue, could hardly be explained by the action of this current. 
 
 If the germs were mechanically transported, why was it that only 
 certain forms, notably saprophytes, were selected ? This cannot be 
 accounted for on the ground of size or independent motility of the 
 organisms. Some forms, such as B. amylovorus, were able to exist in 
 large numbers at inoculation-point for a considerable length of time, 
 
 1 It is possible, however, that a slight amount of fluid may be, drawn up a short 
 distance into the intercellular spaces and vascular lumina, in order to equalize the 
 negative pressure of the contained air which is found often in these cavities. 
 
10 H. L. Russell. 
 
 but did not seem to be able to spread throughout plants which were 
 not its natural host. 
 
 From the above considerations it will be seen that there is no 
 reasonable ground to support the hypothesis that the bacterial distri- 
 bution is purely physical. 
 
 As no actual openings are known to exist in the walls of these 
 cells (if we except the very minute pores through which the plasmic 
 strands pass), it is difficult to understand how the bacteria are able 
 thus to spread from cell to cell unless they possess the power of 
 penetrating the cell wall by the action of vital forces. 
 
 This ability would require physiological activity which could not 
 be present unless they were able to exercise their ordinary metabolic 
 functions. 
 
 This penetrative power, among certain forms, is noteworthy when 
 we compare it with the results obtained by injecting different species 
 into the animal body. 
 
 Von Fodor 1 found that when B. termo, B. subtilis and B. mega- 
 terium were introduced in large numbers into the jugular vein 
 of a living rabbit, they disappeared completely after a lapse of four 
 hours. 
 
 Wyssokowitsch 2 also determined that the time necessary to com- 
 pletely destroy all bacteria contained in one c.c. of culture fluid, 
 when introduced into the animal body, varied from 15 min. with 
 Spir. tyrogenum to 7 hours with B. acidi lactici. 
 
 The rapid disposal of these forms in the animal body is correlated, 
 as Nuttall 8 has shown, with the germicidal property of the blood- 
 serum. The action of plant-tissue upon bacteria* is in no case com- 
 parable to this, and would suggest that the plant is not protected in 
 a similar manner. This point will, however, be considered in detail 
 under another head. 
 
 The possible explanation for the upward distribution of germs 
 may rest upon the principle that growth always follows the lines of 
 least resistance. Not only are food materials more abundant in the 
 rapidly growing apex, but the thinner and less developed cellulose 
 walls offer much less resistance to the spread of the germs than the 
 more matured cell-membranes of the older tissue. 
 
 1 Von Fodor : Arch. f. Hyg. IV (1886), 129. 
 
 2 Wyssokowitsch : Zeit. f. Hyg. I (1886), 3. 
 3 Nuttall: Zeit. f. Hyg. IV (1888), 353. 
 
Bacteria in their Relation to Vegetable Tissue. 11 
 
 Can bacteria penetrate the intact healthy tissue of the plant ? 
 In considering this question we may disregard, in this connection, 
 those cases where bacteria have gained access to the inner tissues by 
 means of wounds, and have been able to live there for a certain time. 
 The question as stated above is of practical importance in pathology, 
 for if micro-organisms are able to penetrate the intact tissues, this 
 will explain the way in which infectious material may be distributed 
 from plant to plant. 
 
 The epidermal tissues of the plant are much more resistant to 
 external influences than the parenchymatous elements. This is due 
 to an outer layer of pure cutin, or to the impregnation of the cellu- 
 lose walls with cutinized layers. This resistant sheath is replaced 
 in the older plant by a thicker and more resistant corky layer. 
 These protecting tissues are not perfectly continuous over the 
 exterior of the plant, but are pierced by numerous small openings, 
 the stomata, which afford a direct communication between the sur- 
 rounding atmosphere and the inner cells of the plant. 
 
 What is now to prevent the entrance of micro-organisms through 
 these minute openings in the outer membrane? 
 
 As regards fungi we know that some species, such as Cystopus 
 candidus, the common white rust of Cruciferse, do gain access to 
 the inner tissues, first, by sending their germ-tubes through the 
 stomata into the intercellular spaces. As these spaces are devoid of 
 nutrient material, they must offer but poor conditions for growth 
 to any organism that is not able to extract its nutriment from the 
 living cell, either by haustoria or by penetrating the wall and, by 
 means of ferment action, obtaining access to the protoplasmic 
 materials of the cell. 
 
 With bacteria that are not adapted for a parasitic existence in plant- 
 tissue it is not yet definitely determined whether they can enter by 
 means of these natural openings. I was unable to isolate from the 
 tissue of different plants any bacteria, although the pots and their 
 plants were watered for several days with dilute infusions of the 
 different germs. The results I obtained are not at all in harmony 
 with those of Lominsky, who found that wheat could infect itself 
 naturally in soil seeded with different species of bacteria. Not only 
 was he able to isolate from the roots of the growing plant all the 
 species which he added to the soil, but he found them also in the 
 
12 H. L. Russell. 
 
 tissues of the stem and leaves. This result would have been much 
 more convincing had he used larger plants than wheat, as it is quite 
 possible that the bacteria isolated came from the surface rather than 
 the inner tissues of the plant. 
 
 Although it is extremely doubtful if those micro-organisms 
 whose mode of nutrition is not adapted for parasitical existence in 
 vegetable tissues, can enter the plant without the intervention of 
 an actual wound, it is much more probable that those forms naturally 
 parasitic on plants may sometimes succeed in thus getting a foothold 
 in the tissues. 
 
 Bolley, 1 in his work on surface scab of potatoes, tried the experi- 
 ment of infecting sound, healthy, growing tubers with liquid cultures 
 of the scab bacilli. The growing tubers, after thorough cleansing, 
 were immersed in a fluid containing an infusion of the scab bacilli, 
 and the glass vessel was then protected from outside contamination. 
 In thirteen days the tubers so treated had decayed, while a control test 
 with sterilized water showed tubers perfectly sound and the water 
 clear. He reasons from this that the bacteria penetrated the growing 
 lenticels of the tuber. He also repeated the experiment by saturating 
 with an infusion of scab bacilli sterilized soil in which he transplanted 
 the growing tubers. Control tests, watered with distilled water in- 
 stead of the diluted culture, were made, and he found that infection 
 took place when the bacteria came in contact with the healthy tuber. 
 
 With the pear-blight germ I have found it impossible to infect even 
 the young budding leaves and stems of the pear, when these organs 
 were several times sprayed with a culture of the germ. Susceptible 
 as well as refractory varieties failed to succumb to the disease when 
 subjected to this manner of infection. Atomizing the flower clusters, 
 however, usually yields positive results, according to Waite. Here 
 the tissue is thinner walled, and in some places, as the nectary, is 
 destitute of cutin, so that the bacteria have less difficulty in effect- 
 ing an entrance. The highly nutritious nectar affords them an 
 excellent medium for growth, and here they are able to thrive until, 
 as Waite has suggested, they get a foothold. It is quite possible that 
 this intermediate stage of development affords an opportunity for 
 the accumulation of a ferment by which the germs are able to more 
 easily penetrate the subjacent tissue. 
 
 1 Bolley : Agric. Science, Vol. IV, 250. 
 
Bacteria in their Relation to Vegetable Tissue. 13 
 
 Infection experiments with Galloway's oat-disease succeeded 
 usually with young plants when they were simply sprayed, but older 
 and more developed plants failed to "take" the infection this way. 
 This may possibly indicate that the stomata do not function as a 
 means of entrance, as the older plants are furnished with these 
 structures as well as the young seedlings. 
 
 Kellerman thinks that Bac. sorghi is able to penetrate the roots of 
 the sorghum cane, as the young roots are often attacked during the 
 disease, the infection coming apparently from the soil. Whether 
 they pierce the epidermis itself, or enter by means of the root-hairs, 
 he did not determine. Beyerinck found that through the root-hairs 
 of the Leguminosse, Bacillus radicicola was able to enter and cause 
 the formation of tubercles. 
 
 THE ACTION OF BACTERIA WITHIN THE TISSUES. 
 
 How are bacteria able to spread throughout the tissues of the 
 plant ? We have seen, in the results already detailed, that with certain 
 forms, mainly saprophytic, they are able to pass from cell to cell. 
 That they do this in plant-diseases is evidenced by the lesions that 
 they call forth. But just how they are able to make their way from 
 cell to cell is by no means so evident. In the light of our present 
 knowledge concerning the transpiration stream, we cannot conceive 
 of this current being utilized as a bearer of solid particles unless they 
 have an inherent power of penetrating the cell wall. We do not find 
 that the bacterial plant-diseases are able to spread their infective 
 material throughout the plant in a manner comparable to a septi- 
 caemia, which is often developed in animals. This they would be 
 able to do if the transpiration current could function, like the blood 
 stream, as a distributor of infection. 
 
 It is possible that the lumina of the vascular tissue afford the 
 least resistance to the spread of infection, yet, so far as .we now 
 know, only one parasitic species has adapted itself to this course. 
 Wakker's Bac. hyacinthi affects primarily the xylem tissue of the 
 fibrovascular bundle. Not only does it occupy the cavity of these air 
 cells, but also attacks the surrounding walls, chiefly the middle 
 lamella, which it soon converts into a disorganized gummy exudate, 
 and is thus able to spread to the surrounding tissue. 1 Through these 
 
 1 Wakker: Arch, neer., T. XXIII, p. 6 (1888). 
 
14 H. L. Russell. 
 
 elongated vessels it is able to spread the disease quite rapidly, as 
 has been demonstrated by artificial infection experiments. 
 
 The rapidity with which the pear-blight germ is able to spread its 
 infective material through a susceptible host also indicates a very 
 rapid movement from cell to cell. This is especially marked in the 
 softer succulent tissue of the youngest twigs and in the blossoms. 
 After once securing an entrance to the rapidly growing tissues, it 
 sets up a kind of fermentation which completely destroys many of 
 the cells, thus forming large spaces which are filled with the gummy 
 products of its fermentative activity. Under favorable conditions, 
 the rapidity with which the blight bacteria spread is quite surprising. 
 The following laboratory note may be considered fairly indicative of 
 the rate of distribution. March 8, a Japan seedling was infected by 
 puncture of the young stem. March 13, the disease had manifested 
 itself by a local blackening of the tissue in the neighborhood of the 
 inoculation point. Two days later, the stem showed that the 
 disease had progressed fully six inches from point of inoculation, as 
 indicated by blackened appearance. The presence of bacteria was 
 also demonstrated microscopically fully an inch or more beyond 
 this blackened tissue, showing that the spread of the disease, after 
 having once established itself, was quite rapid. 
 
 It has been suggested that bacteria are able to pass from cell to 
 cell through minute pores in the walls. Recent investigations 1 show 
 that the direct union of the plasma of cell to cell is very much more 
 widely diffused than was formerly supposed, and that all the living 
 elements of the whole plant-structure of higher plants are thus united. 
 
 These plasmic strand-connections vary in diameter from 0.05-1.0^, 
 but on the average they are so small that it would seem hardly 
 possible that they coul^ be utilized by the bacteria in forcing their 
 way from cell to cell. It seems much more probable that their 
 progress is effected by ferment activity. In the case of the pear- 
 blight germ and the hyacinth-disease, it is seen that the healthy 
 tissue undergoes a decomposition under the influence of the bac- 
 teria, resulting in the production of a gummy substance, and in the 
 case of the blight, the liberation of CO 2 . 
 
 Bolley 2 finds the germ causing the surface scab in the potato im- 
 
 1 Kienitz-Gerlofi : Bot. Zeit. (1890), XLIX, 1. 
 
 2 Bolley : Agric. Science, IV, 284. 
 
Bacteria in their Relation to Vegetable Tissue. 15 
 
 bedded in the protoplasm of the cell. In this case the cell mem- 
 branes were seen to be actually eroded by the bacillus. 
 
 A similar condition is found with B. olese-tuberculosis in the 
 olive, and B. Veuillemini in the tumors of Pinus halapensis, where 
 actual destruction of cell walls is accomplished under the influence 
 of the germ. It is not at all improbable that those species which 
 are adapted to a parasitic existence in the plant organism may not 
 possess an eroding or fermentative ability, which would enable them 
 to break down the resistant cell walls which impede their spread. 
 
 But how do we find it with those forms which are not so 
 thoroughly adapted to this kind of life ? It is much more difficult 
 to determine the distribution in these cases than it is where the germ 
 is able to grow luxuriantly. With the results which were obtained 
 from the inoculation of those micro-organisms that are incapable of 
 producing a genuine infection in plant-tissues, it has been shown in 
 several cases that there was a distinct tendency to spread throughout 
 the plant to a certain extent. These bacteria, which were deter- 
 mined at greater or lesser distances from the inoculation point, 
 were also definitely located in the interior of the cells. This condi- 
 tion was best seen with cultures of B. acidi lactici, but was also 
 recognized with B. luteus, B. pyocyaneus, and B. fluorescens. As 
 has already been said, we cannot explain their presence unless they 
 are able to pass through the cell walls. No openings of any kind 
 could be determined, and the only remaining possibility that sug- 
 gests itself is that they have the power, by means of a ferment 
 excreted, to work their way from cell to cell without causing a 
 permanent rupture. This we know to be the case with certain 
 Ustilaginese. They can penetrate the cell wall, which, after the 
 passage of the hypha, again closes, so that no opening is apparent. 
 With as small a structure as a bacillus this process is also con- 
 ceivable. This explanation, however, does not rest upon experi- 
 mental proof and is only suggested as a possible hypothesis. 
 
 RESISTANCE AND IMMUNITY OF PLANTS TOWARD BACTERIA. 
 
 The general exemption of plants from bacterial attack, which was 
 referred to in the introduction under the expression "Immunity/' 
 reveals, upon a closer consideration of the question, a series of 
 
16 H. L. Russell 
 
 phenomena of a complex order. In the appendix to this paper will 
 be found a complete list of all the plant-diseases which are now 
 known to be closely associated with bacteria. A complete com- 
 pilation of this sort has not previously been made for the bacterial 
 diseases of plants, and a tabular review of this field of bacteriology 
 was thought to be desirable. Although the causal relation between 
 a specific organism and a plant-malady has not in every case been 
 satisfactorily and thoroughly demonstrated, there is no doubt but 
 that most of the plant-diseases mentioned may be rightfully ascribed 
 to the ravages of these micro-parasites. When we consider how 
 little attention has been paid to this branch of phytopathology, it 
 is no wonder that our information on this subject is meager. 
 
 The list of diseases, although now limited, is rapidly and con- 
 stantly increasing, so that we may freely predict that with a more 
 thorough and exhaustive study of plant pathology from a bacterio- 
 logical standpoint, the number of diseases will be materially aug- 
 mented. Even now we possess sufficient data to qualify the 
 assertion that plants are not subject to diseases of a bacterial origin. 
 
 A closer study of the general exemption of plant-structures from 
 the attacks of micro-organisms reveals the fact that the phenomena 
 heretofore embraced under the general term of immunity, are not of 
 the same character in all cases. Different phases of this exemption 
 seem to exist. One of these is the reaction of the plant toward 
 micro-organisms in general. The other is the ability of certain plant- 
 structures to withstand the inroads of a particular bacterial parasite. 
 Under the first head, the micro-organism is unable to gain a foot- 
 hold in the tissue of the plant, or, having once gained an entrance 
 accidentally, it is unable to cope successfully with the repellant 
 forces resident in the tissues. There is no susceptibility on the part 
 of the plant toward the germ in question. This is the action which 
 living tissue exerts in general. Where this action is overcome and 
 the micro-organism triumphs, we have the development of disease. 
 
 Now, the ability of a single individual to withstand the attacks of 
 a germ capable of producing a disease in the tissue of another indi- 
 vidual of the same species, is evidently a different action. There 
 is a certain degree of susceptibility on the part of the plant to suc- 
 cumb to this enemy, as is evidenced by the fact that when the con- 
 ditions which maintain the natural balance of the forces inhibiting 
 the germ are disturbed, the germ is then able to successfully attack 
 
Bacteria in their Relation to Vegetable Tissue. 17 
 
 the weakened plant. To this latter class of phenomena it would 
 seem proper to limit the term immunity. 
 
 We would scarcely consider the human body immune from the 
 attacks of ordinary saprophytes, even those forms which are normally 
 found in the oral cavity. Most of them seem to possess no ability to 
 thrive inside of the animal organism, but find their natural condi- 
 tions of existence in the dead organic material which is always 
 present in the mouth. Likewise, it would seem improper to say 
 that a rose is immune from Bac. tuberculosis because the tubercle 
 bacilli do not find in the tissues of the plant the necessary conditions 
 for their development. 
 
 While the bacterial parasites already known are sufficient to indi- 
 cate that we cannot consider the vegetable kingdom as wholly free 
 from bacteria, yet we must admit that the susceptibility of plants 
 is very much less than that of animals. 
 
 In considering, then, this exemption of plants from the attacks of 
 micro-organisms, we will divide the phenomena into two classes : 
 
 First, those due to what may be called Resistance; second, those 
 due to Immunity. 
 
 Before going farther, it will be necessary for us to determine the limi- 
 tations which will be imposed upon the meaning of these two terms. 
 
 The inherent power of the vegetable organism to withstand the 
 action of bacteria in general may be termed Resistance. This resist- 
 ance which the plant offers to the entrance of micro-organisms may 
 be due to various causes, and is operative throughout the whole range 
 of plant life. It is the normal condition of the plant, and is closely 
 correlated with the conditions of nutrition, for when the natural play 
 of these forces is disturbed, and an abnormal state of affairs super- 
 venes, this power of resistance may be subject to greater or less modi- 
 fication. This lowering of the general vitality of the plant, due 
 possibly to a number of causes, is usually manifested in a lessening of 
 the powers of resistance which the plant seems to possess. The plant 
 organism becomes then more susceptible to the attacks of disease. 
 
 This state of affairs must not be confounded with a condition 
 which affords a more favorable opportunity for the development of 
 the attacking parasite. The one concerns itself with those processes 
 which tend to lower the general vitality, and thus the resistance of 
 the plant ; the other relates only to those conditions which give 
 
18 H. L. Rmsell 
 
 increased powers of development to the attacking organism. It is 
 possible that the same set of causes may produce this double effect, 
 as, for instance, such meteorological conditions as excessive moisture, 
 to the extent that it not only interferes with the normal action of 
 the vital processes of the plant, but gives also the optimum condi- 
 tions for the development of the parasite. But while the resultant 
 of these forces may have a doubly deleterious action on the plant, it 
 does not of necessity follow that this should be the case. 
 
 It will have been seen that the resistance which a plant offers 
 toward its enemies in general is broad and wide-reaching in its effects ; 
 not so with immunity in regard to a specific disease. The one is a 
 general condition of normal, healthy vegetable life ; the other, the 
 expression of a restricted group of vegetable organisms toward the 
 cause of a specific malady. The term immunity will then be restricted 
 to those plant-organisms which do not succumb to the action of a 
 germ that is able to call forth a genuine infection in another related 
 species. Thus we may define Immunity in plants as the ability of 
 the organism to repel the attacks of a germ which produces a path- 
 ological condition in a closely allied form. By a closely allied form, 
 we mean a species or variety which stands in close taxonomic affinity 
 with the form which is a natural host for the germ in question. 
 Now, the limit of this immunity must, of necessity, be a somewhat 
 variable one. Whether the term should be restricted in its applica- 
 tion to those species grouped in the same genus or subgenus, or 
 whether it should embrace the limits of a whole family, will differ in 
 different cases. 
 
 Our knowledge of the ability of bacterial germs to produce in 
 plants a diseased condition in different species is yet somewhat 
 limited, but the observations already on record are further strength- 
 ened by analogous cases with fungal diseases. 
 
 We know that some fungi are very restricted in their development, 
 and that outside of a single host-plant they are unable to call forth 
 any diseased condition, even under the most favorable opportunities. 
 This is the case with Fusicladium pirinumj which causes the destruc- 
 tive pear-scab both in this country and Europe. Sorauer 1 claims 
 that under no conditions, even during the seasons which are most 
 favorable for the growth of the fungus, does it ever exceed the 
 
 1 Sorauer : Landw. Versuchsstat. XXVI, 327. 
 
Bacteria in their Relation to Vegetable Tissue. 19 
 
 narrow limits which form apparently its fixed boundaries. On the 
 other hand, the host-distribution of some diseases is known to be 
 dependent largely upon certain climatic conditions. During years 
 with the normal amount of rainfall or seasons of drought, the fungi 
 only attack the ordinary hosts upon which it is a natural parasite, 
 but when an excessively rainy season supervenes, the conditions 
 being then much more favorable for the development of the parasite, 
 the fungus is reported upon many new hosts, usually, however, 
 allied species within generic or tribal limits. Swingle 1 gives an inter- 
 esting series of results which he found with the Peronosporese on 
 the Euphorbise in Kansas, corroborative of this statement. Here 
 the ordinary boundaries which usually limit the spread of the fungus 
 were broken over during those years that were particularly favorable 
 for the development of the parasite, and the same parasitic species 
 was often found on entirely new hosts. 
 
 These two extremes indicate the impossibility of establishing any 
 hard and fast line for the limits of a disease, and, consequently, the 
 limits of immunity in the latter example would be much wider than 
 in the former. 
 
 So far as is at present known, among the bacterial plant-diseases 
 we have no malady that is able, either in a state of nature or by arti- 
 ficial injection, to produce a pathological condition in plants belong- 
 ing to different natural families. Such a condition may not be 
 impossible, however, and further research may give us examples 
 which have a wider range of host-plants. The majority of them are 
 naturally limited in their distribution, even within generic and often 
 within specific boundaries. 
 
 The two phases to which this exemption of plants from bacteria 
 is due, immunity and resistance, although acting distinctly with 
 reference to different germs, may be resident even in the same plant 
 organism. A plant may be resistant or totally insusceptible toward 
 an ordinary saprophyte or even a bacterial parasite whose host-plant 
 is in a distant family, and yet may or may not possess immunity 
 from another species of bacteria which is a natural parasite upon a 
 closely related species. 
 
 The presentation of a few examples of what is meant by this will 
 suffice to illustrate this distinction between immunity and resistance. 
 
 'Swingle : Kans. Acad. of Science, Vol. VI, 1887-88. 
 
20 H. L. Russell. 
 
 Reference must again be made to the pear-blight germ (B. amylo- 
 vorus), as its biology is the most thoroughly investigated of any of 
 the bacterial plant-diseases. So far as is known, this malady is con- 
 fined strictly to the Rosacea?, and almost without exception to the 
 sub-order Pomese. It has been reported to have been found in the 
 young fruit of the Kelsey plum 1 (Primus sp.), where it was traced to 
 the sting of a curculio, when the eggs were deposited, and also in a 
 new disease of rasp- and blackberry. 2 However, this last exception 
 has not yet been thoroughly demonstrated. Arthur also reports that 
 he was able to produce a slight infection in the succulent shoots of 
 the peach, but not at all in other non-rosaceous fruits, as mulberry 
 and grape. 3 While the disease afflicts several different species of 
 Pomea3, its commonest host is the cultivated pear. The early history 
 of this disease shows that it was at first more or less restricted in its 
 development on this species, attacking only certain varieties, but in 
 the wider range of the malady in later years, it seems to have 
 acquired the ability of successfully attacking other varieties, until 
 now we know of no variety that is absolutely immune, in the state 
 of nature, from the disease. Although not wholly immune, many 
 horticultural strains possess immunity in a partial degree, as is evi- 
 denced by the fact that under like conditions certain varieties yield 
 much more readily to the disease than others. By some peculiarity 
 in the structure of the plant, possibly merely mechanical in its 
 nature, one variety is able to successfully resist the attacks of the 
 parasite to a larger extent, and thus possesses a partial natural 
 immunity from the disease. 
 
 This immunity can often be overcome, however, if the germs are 
 able to gain access to the tissues in some manner, as by wounds from 
 insect stings, etc. 
 
 This is well shown by the following greenhouse experiment : 
 
 Set 1. Two pear trees (Japan seedlings 4 ), 2 years old, were inocu- 
 
 1 Personal communication from Mr. M. B. Waite, to whom I am indebted for a 
 number of facts bearing on this topic. 
 
 2 Detmers: Ohio Bull. Exp. Stat., No. 6, Oct. 1891. 
 
 3 Arthur: N. Y. Ann. Agri. Exp. Stat., 1884, 362. 
 
 4 This stock, lately introduced from Japan, is in great favor with nurserymen on 
 account of its vigorous and luxuriant growth, and its seeming refractory qualities, 
 under ordinary conditions, toward the blight. Growers have, however, not had 
 experience with it long enough to determine whether its seeming good qualities are 
 of a permanent nature or not. 
 
Bacteria in their Relation to Vegetable Tissue. 21 
 
 lated with B. amylovor us, sub-epidermally, on March 3. March 12, 
 the blight was well marked as a blackened patch for nearly an inch 
 on each side of point of inoculation. Period of incubation, therefore, 
 9 days. 
 
 Set 2. Two 2-year old' trees, of blight-proof variety, budded 
 on Japan stock, were inoculated, sub-epidermally, March 17. Evi- 
 dence of blighting in leaves and stems readily recognizable on 
 March 25. Incubation period, 8 days. 
 
 Set 3. 2-year old budded Clapp's Favorite (a variety readily sus- 
 ceptible to the disease in the orchard) was inoculated in the same 
 manner, March 3. March 12, diseased condition apparent, although 
 not as well marked as in Set 1. Period of incubation, 9 days. 
 
 From this set of experiments, it will be noted that those varieties 
 (Sets 1 and 2) which under natural conditions are known to be much 
 more refractory than others (3), not only lost their partial natural 
 immunity when subjected to artificial inoculation, but yielded to the 
 disease fully as quickly as did the variety that was naturally sus- 
 ceptible. This artificial inoculation is, however, a much severer test 
 than they receive under the operation of ordinary conditions of 
 cultivation, but it shows that the varying degrees of susceptibility, or, 
 in other words, immunity can be overcome under certain conditions. 
 
 Waite attempted to infect two different species of Cratsegus (C. 
 oxyacantha and C. tomentosa, var. parviflora) by atomizing the 
 flowers, but found that only the latter succumbed to the action of the 
 germ. Here again is a case of immunity where one variety is exempt, 
 under certain conditions, from the disease. The immunity in this 
 case is, however, not a deep-seated condition, as is shown by the suc- 
 cessful infection of the latter variety by puncture inoculation, where 
 the bacteria were actually introduced into the tissues. Other species 
 of the pomaceous group of the Rosacese are more or less susceptible 
 to the disease, although much less so than the pear and apple. The 
 cultivated species of this fruit family seem to be more readily suscep- 
 tible than many of the wild species. Certain species, such as the 
 Haw (CrataBgus spp.) and Shadbush (Amelanchier Canadensis), are 
 subject to the disease when artificially inoculated with the germ. 
 
 The researches of Savastano 1 on the tubercle of the olive tree in 
 Italy also aptly illustrate the relation of immunity and resistance. 
 
 1 Savastano : Tuberculosi, iperplasie, e tumori dell' olivo : Ann. R. Scuola Sup. 
 d'Agric., Vol. V, 1887. ^T\ 
 
 ur 
 
22 H. L. Russell. 
 
 The bacillus causing this disease produces an hypertrophy of the 
 cambial and extra-cambial tissue, which is, however, quite local- 
 ized. The results of artificial inoculation into young olive trees 
 were evident in 25 days, and in 2 months a well-marked swelling 
 was to be noted at seat of inoculation. Savastano was not able, 
 however, to successfully infect, in equal degree, all varieties of this 
 species, but found a varying degree of susceptibility in different 
 varieties. When the B. olese-tuberculosis was injected into other 
 healthy fruit-bearing trees, such as lemon, bitter orange, pear, apple, 
 quince, etc., no trace of the infection could be noticed. Here is, then, 
 a case of resistance against the organism even though it was a para- 
 sitic organism on other forms of plant life. 
 
 He also infected olive trees in like manner with several other 
 micro-organisms which he found associated in the tuberculous 
 growths with the true cause of the disease, but in no case was 
 any pathological condition brought about, showing that the normal 
 resistance of the plant was able to overcome the accompanying sap- 
 rophytic micro-organisms, although it was not able to withstand the 
 attacks of the parasite in all cases. 
 
 The examples already cited will suffice to show the distinction 
 made between immunity and the normal resistance of the plant, and 
 also that immunity is a varying term itself, sometimes applicable 
 within narrow limits, then again spreading over a greater variety of 
 species. Not only are the limits of immunity ill-defined and vary- 
 ing, but the degree of immunity also varies considerably. This is 
 readily recognized in horticulture, when we say that one variety is 
 more susceptible to the attacks of a certain disease than another. 
 This variation of the susceptibility of different varieties indicates 
 that they possess an immunity to a greater or less extent from the 
 action of a definite specific germ. 
 
 We might consider, also, other phases of immunity which present 
 themselves for consideration, but a mere mention of these will be 
 all that can be given of them in this connection. Thus we have the 
 local immunity, which certain tissues enjoy against the attacks of 
 micro-parasites as they increase in age and consequently become 
 better developed and more resistant. This rests on a purely physical 
 basis, and the importance of it will be considered later more in detail. 
 This local immunity of certain tissues is strongly reinforced, also, 
 
Bacteria in their Relation to Vegetable Tissue. 23 
 
 by a consideration of the phenomena connected with certain fungal 
 diseases, as in the case of Cystopus Candidas, which, according to 
 De Bary, can only successfully infect the host-plant when it enters 
 the young cotyledons of the plant. Hypoderma macrosporon is 
 only able to gain entrance into the pine through the young pine 
 cones. 
 
 This law usually holds in connection with the bacterial plant- 
 diseases. Most of them are more virulent in their course when they 
 attack young and undeveloped hosts, and not a few are apparently 
 inhibited after the tissues have reached a certain stage of maturity, 
 as in the case of the oat-disease of Galloway and the pear-blight. 
 
 CAUSES OF IMMUNITY AND RESISTANCE. 
 
 Having cited special cases illustrative of resistance and immunity, 
 we may now turn to the consideration of the possible factors which 
 are able to cause these conditions. To this difficult problem we can- 
 not hope as yet to give any definite and conclusive answer. The rapid 
 progress which has been made in this department of animal biology 
 within the past five years indicates how vast and complicated the 
 question is in all its bearings. The accumulating data which have 
 already been collected have, however, contributed much to a better 
 conception of the problem of immunity, and lead us to believe that 
 any experimental consideration of this subject in relation to plants, 
 even though negative in its results, is not entirely without value. 
 
 The attempt has been made in the previous pages to show that 
 there are two factors at work in the struggle of the plant with its 
 parasitic enemies. We shall not, however, attempt to prove that the 
 phenomena which are considered as resistance and immunity are 
 brought about through the action of separate and distinct forces. It 
 is possible, and quite probable, -that the conditions which produce 
 one factor may also be the cause of the other. For instance, in 
 animal biology, Wyssokowitsch determined that certain saprophytes, 
 as well as some parasites, disappeared completely when introduced into 
 the blood of a living rabbit. Nuttall determined that the cause which 
 destroyed saprophy tic as well as pathogenic organisms was the same, 
 namely, the germicidal property of the body fluids. Although the 
 result was brought about through the operation of the same cause, 
 
24 H. L. Russell. 
 
 we would not consider these two cases similar. The one is simply 
 the normal resistance which the animal offers to an organism which 
 has no power under any circumstances to produce a diseased condi- 
 tion in its body. The other is a case of immunity to a certain 
 degree against the pathogenic organism. 
 
 We cannot, however, compare the phenomena of animal immunity 
 too closely with that of plants, as we find that the causes which tend 
 to produce this state are unlike in the two kingdoms. A much 
 closer similarity exists between the immunity of plants from bacteria 
 and from fungi. Not only are the phenomena presented quite 
 homologous in character, but the causes which are operative are no 
 doubt more or less closely related. 
 
 It will be hardly possible to classify the causes which may tend 
 to produce the resistance and immunity of the plant from its bacterial 
 foes in any satisfactory and complete manner. A tentative classifi- 
 cation, however, may be suggested along the lines of physical and 
 chemical action ; including under physical sources all those mechan- 
 ical contrivances, such as epidermal covering, cutinization of tissues, 
 and the secondary thickening and lignification of cell membranes, 
 which enable the plant to ward off injurious external forces. Under 
 chemical sources we would class, not only the reaction of the tissues 
 and the nutritive conditions, but the resistant action due to the living 
 protoplasm itself. 
 
 That one of the possible causes of the partial immunity which 
 some plants exercise toward parasitic forms is dependent largely 
 upon the mechanical obstructions which the plant offers to the 
 entrance of the germ, is seen in the examples of immunity which 
 have already been mentioned. 
 
 Certain strains of the common pear, under ordinary conditions of 
 cultivation, are quite refractory toward the blight when subjected to 
 natural infection which takes place in the blossom through insect 
 visitation, but these varieties when artificially inoculated sub-epider- 
 mally with bacteria yield readily to the disease. This can scarcely 
 be accounted for on any other ground than that the blight bacteria 
 are unable to gain a foothold on account of some peculiarity of the 
 external plant membranes. This may be so slight that one cannot 
 detect any histological difference in the exterior cells, yet one variety 
 will be considerably more refractory under natural conditions than 
 the other. 
 
Bacteria in their Relation to Vegetable Tissue. 25 
 
 Arthur 1 has drawn attention to this point and suggests that these 
 differing degrees of susceptibility are due to physical causes. 
 
 Not only has mechanical exclusion, as a cause of immunity, been 
 shown in the pear-blight disease, but other bacterial diseases, as well, 
 illustrate the operation of this cause. In his inoculation experi- 
 ments upon " La Jaune des Jacinths," Wakker 2 infected, besides a 
 number of susceptible varieties of the hyacinth, one variety (Norma) 
 which was regarded under natural conditions as immune from the 
 disease. This he found succumbed as readily to the malady as the 
 naturally susceptible varieties when the infective material was 
 introduced into the leaf of the plant, showing that the natural immu- 
 nity of the variety was dependent upon its epidermal tissue. 
 
 These two cases, cited above, are examples where immunity of the 
 plant toward a specific parasite is dependent upon a physical means 
 of exclusion, but the same cause is also operative in regard to the 
 general resistance of the plant against all forms of germs. Under 
 ordinary circumstances we do not find that saprophytic organisms, 
 even decomposition bacteria, are able to enter the normal, healthy, 
 intact plant structure, yet we have shown in the preceding pages 
 that these germs when they once get a foothold into the plant tissue 
 are able to survive for a long time, and where the vitality of the 
 host is much reduced may even cause a disorganization of tissue. 
 
 If the thin cutinized layers of epidermal cells afford such an effectual 
 barrier to the entrance of micro-organisms, the more resistant corky 
 layers of the mature plant will be even more efficacious in excluding 
 germ life in general. This is demonstrated by the complete inability 
 of most bacterial diseases 8 to penetrate the resistant tissues of the bark. 
 These act as an efficient barrier against the entrance of any organisms, 
 except through the natural openings (lenticels) and wounds. 
 
 Although the cuticular and cortical layers of the plant function 
 as the chief hindrances to the entrance of germs, fungal as well as 
 bacterial, the fully developed walls of the inner cells also inhibit 
 the spread of pathogenic forms. The young fruit of the pear 
 cannot be successfully infected after it has reached a certain size, as 
 
 'Arthur : Proc. Phil. Ac. Nat. Sc. 1886, p. 340. 
 
 2 Wakker: Arch, norland, d. Sc. ex., T. XXIII, p. 18. 
 
 3 Savastano thinks that B. olese-tuberculosis must make its way through the bark 
 tissue in order to reach the succulent cambium where it thrives. But this idea is 
 conjectural and is not based upon experimental proof. 
 
26 H. L. Russell. 
 
 the tissues become so mature that the germ is not able to pass 
 from cell to cell. It is also particularly prominent in the blighting 
 stem, where the disease is usually confined to the youngest, most 
 succulent tissue. This is characteristic of bacterial plant-diseases in 
 general, that the most pronounced lesions are always found in tissue 
 which has not yet lost its power of growth. 1 
 
 We turn now to consider the chemical sources of protection which 
 the plant may possess against its enemies. First of all we have the 
 chemical reaction of the plant-tissues. As was noted in the intro- 
 duction, it is to this source that most authors ascribe the general 
 freedom of plants from bacteria. This was before it was thoroughly 
 proven that vegetable structures were affected to any extent by bac- 
 terial diseases, and was probably based upon the then prevailing 
 idea that bacteria required alkaline and fungi acid substrata for 
 their development. So many exceptions to this law are now known 
 that this statement has lost much of its original force. Most of those 
 forms which we know to be able to cause bacterial plant-maladies 
 are usually more or less indifferent to the reaction of the medium, 
 growing in either weakly acid or alkaline nutrient media. Arthur 
 succeeded in raising B. amylovorus in 2 per cent malic-acid bouillon. 
 
 The experiments already detailed indicate that saprophytes, and 
 even some animal pathogenic forms, are not destroyed by the plant 
 juices either within or outside of the plant. Forms like B. prodi- 
 giosus, B. lac. aerogenes, B. megaterium, B. coli commune, Kiel 
 water-bacillus and blue pus germ grew in the expressed plant juices of 
 various kinds and produced a considerable turbidity in 24-48 hours. 
 
 It would seem, then, that the importance of this factor as the 
 prime cause of immunity and resistance has been considerably over- 
 estimated. Very much more stress is to be laid upon the mechan- 
 ical barriers which the plant possesses against the entrance of germs, 
 as well as the activity of the living protoplasm. 
 
 The nutritive conditions offered by the plant may also be con- 
 sidered in this connection. While the dead tissues of many plants 
 
 1 The observation which Prillieux noted in the case of B. Vuillemini, which causes 
 the tumors in the old wood of the Aleppo pine (Pinus halapensis), is only apparently 
 contradictory. The fact that a local hypertrophy of tissue was produced by means 
 of the bacterial stimulus showed that the tissues were yet in a secondary meri- 
 stematic condition. 
 
 2 Zopf: DiePilze, S. 173. 
 
Bacteria in their Relation to Vegetable Tissue. 27 
 
 afford a tolerably good substratum for the development of many 
 species of bacteria, and thus show that the tissues are not wanting 
 in the necessary nutritive materials, the conditions are different in 
 the struggle between the disease germ and the living plant. Unless 
 the germ is able to gain access to the inner tissues by means of acci- 
 dental lesions, it must force its way through the epidermal cell 
 walls, or the cell membranes of the interior tissue, either directly 
 from the outside, or after having first gained an entrance through 
 the stomata into the intercellular spaces. In either case it has no 
 supply of nutrient material with which to carry on its metabolic 
 activity, and is therefore unable to gain a foothold from which to 
 develop. 
 
 If the bacteria could increase in sufficient numbers on the surface 
 of the plant they might be able to penetrate the tissues more easily. 
 That B. amylovorus is in this way able to gain access to the tender 
 tissues of the receptacle of the pear-flower is extremely probable. 
 The sugary secretions which are poured out by the nectariferous 
 glands in the flower induce insect visitation, and afford the best 
 possible medium for the growth of the bacilli which are brought to 
 it in the sticky exudate which adheres to the insect. Thus the 
 bacteria have a fertile soil prepared for their further development, 
 and are able to multiply with ease. Having thus secured such a 
 coigne of vantage, they are able to penetrate the non-cutinized tissues 
 beneath, and thus gain entrance to the inner parts of the plant. 
 
 Do plant juices possess germicidal properties f 
 
 Recent experiments in animal pathology have demonstrated that 
 the blood of many animals possesses the property of destroying 
 bacteria to a limited extent, either when brought directly in contact 
 with it in the body of the animal, or after it had been aseptically 
 removed. This bactericidal power of the blood enables the animal to 
 destroy, not only the saprophytic forms with which it comes in con- 
 tact, but also a certain number of even malignant bacteria, which 
 otherwise would be able to multiply in the body and finally produce 
 death. This line of investigation, so fruitful of results in immunity 
 in the animal kingdom, suggested a series of experiments as to 
 whether a corresponding condition might not exist in plant life as 
 well. 
 
 Although we have in plant-tissue nothing homologous to the circu- 
 latory fluids of the animal body, it might be conceivable that the 
 
28 H. L. 
 
 plant fluids were endowed with a gerraicidal property for the pro- 
 tection of the plant. If the plant possessed such a peculiarity, an 
 examination of the cell sap, with this point in view, ought to indicate 
 its presence. The first difficulty to be met with, however, is to 
 secure the cell sap free from solid elements and in an aseptic con- 
 dition. This can be accomplished without serious difficulty in the 
 case of the blood, but as there is no special channel for the move- 
 ment of the plant fluids, the problem here is not so easily solved. 
 
 In a foregoing set of experiments, in which different species of 
 bacteria were artificially introduced into the plant-tissues, it was found 
 in a number of cases, particularly with saprophy tic forms, that they 
 had multiplied to a limited extent. This at first might indicate that 
 the plant-juices had no germ-destroying power. Such a conclusion 
 need not necessarily follow. It has already been found that the 
 germicidal action of the body fluids towards certain organisms has 
 a definite limit, and that when too many germs are brought in con- 
 tact with it its capacity for destroying the bacteria is overcome, 
 and the germs are able to increase and call forth a pathological con- 
 dition in the body. That such might have been the case in the 
 above experiments was possible, as large numbers of bacteria were 
 introduced into the plant. 
 
 To determine this, experiments were carried out on plant-tissues 
 to determine if the plant-juices possessed any germicidal properties. 
 Heating could not be resorted to as a means of sterilization, as this 
 would affect any property analogous to the germ-killing peculiarity 
 of the blood, so the only recourse was to obtain the juices aseptically. 
 Trituration in a small sterilized mortar was first attempted, but this 
 method was regarded as unsatisfactory on account of the cellular 
 detritus present. Expression of the juice was then tried by com- 
 pression. A small screw press, capable of being sterilized, was used 
 for this purpose, and as the fluid escaped through the minute open- 
 ings in the bottom it was caught in a sterilized receiver and pipetted 
 into small culture bulbs as before. By this process the plant-juice 
 was secured perfectly free from solid particles. Into this culture 
 fluid a number of germs were inoculated, as determined by NuttallV 
 device for accurate quantitative work, and at varying intervals of 
 time the germ-contents of the bulbs were determined. In each case 
 
 'Nuttall: Bull. J. H. H. No. 13, May-June, 1891. 
 
Bacteria in their Relation to Vegetable Tissue. 
 
 29 
 
 about 5-7 cc. of the expressed juice was used. The quantitative 
 results, indicated in the following table, show the influence of the 
 plant j uices upon the growth of different species of micro-organisms. 
 
 Name of Germ. 
 
 No. used as 
 "Seed." 
 
 Period of 
 Incubation. 
 
 No. at end of 
 Experiment. 
 
 Plant Juice 
 used. 
 
 Kiel water-bacillus . . 
 
 859 
 26 
 
 2 hrs. 40 min. 
 24 " 
 
 6700 
 8420 
 
 Canna. 
 
 
 
 Bac. lactis aerogenes. 
 B. coli commune 
 
 26 
 26 
 
 46 
 
 5 " 
 24 " 
 
 24 " 
 
 90 
 7200 
 
 12 480 
 
 n 
 it 
 
 1 1 
 
 B meffaterium 
 
 14 
 
 1 hr 45 min 
 
 25 
 
 ti 
 
 
 14 
 14 
 
 20 
 
 7 " 
 10 hrs. 30 min. 
 
 4 it 
 
 215 
 3060 
 
 35 
 
 
 i 
 
 it 
 
 
 20 
 
 105 
 105 
 
 24 " 
 
 4 " 
 24 " 
 
 4600 
 160 
 32,000 
 
 < i 
 n 
 it 
 
 Most of the species which were used in the above experiment are 
 those which showed a marked increase when in the plant-tissues for 
 a considerable period of time. This table, however, indicates that 
 the increase began immediately upon the introduction of even small 
 numbers into the cell sap, showing that this fluid possessed no bac- 
 tericidal properties. 
 
 The attempt to test the action of cell sap was also tried in another 
 way. However, this method did not allow of accurate quantitative 
 determination, although the other conditions were more nearly 
 normal. It was based upon the action of root pressure in the plant. 
 Thrifty young plants with good-sized stems, like the Lima bean or 
 geranium, were selected, and after having washed the stems with a 
 disinfecting solution, they were cut off with a sterile knife about an 
 inch from the ground. The stump of the plant was then quickly 
 covered with a short sterile test-tube, which made a moist chamber 
 that prevented evaporation. The pot was then set in a warm place 
 to induce copious root-action, and in 12 to 24 hours a large drop of 
 cell sap had exuded from the cut end of the stem. This clear fluid 
 was then inoculated with a few germs from a fresh culture, to be 
 tested, and after a varying length of time their relative number 
 determined as nearly as possible. 
 
30 H. L. Russell. 
 
 A marked increase with B. megaterium, B. butyricus, B. coli 
 commune and B. pyocyaneus was noted, while Strept. pyogenes in 
 five days was killed. As the death of the bacteria inoculated did 
 not occur at once, but was gradual, it was no doubt due to unfav- 
 orable nutritive conditions rather than any germicidal effect of the 
 cell fluids. 
 
 The cell sap usually possesses a distinct acid reaction, and would,, 
 no doubt, inhibit the growth or kill out by malnutrition those forms 
 susceptible to acid reaction. Some plant-juices afford a much better 
 nutritive medium than others, such as the sugar-cane or the saccha- 
 rine varieties of sorghum, or the sap of such trees as Acer sacchari- 
 num. Sternberg 1 has recommended the milk in green cocoanuts as a 
 nutritive medium for even animal pathogenic organisms. This i& 
 really the elaborated cell sap of the embryo-sac. 
 
 In the animal body we find that a bactericidal property is not 
 only resident in the blood plasma and tissue juices, but is also found 
 in various secretions and excretions which are formed in the animal 
 organism. 
 
 Thus the sputum of a healthy individual is known to have an 
 anti-bacterial effect on anthrax, 2 while the germicidal properties of 
 fresh milk 8 and urine 4 are quite considerable. 
 
 Although we have been unable to detect any analogous property 
 in the cell sap of the plant, we know that the plant is able in many 
 cases to protect itself by means of its secretions. Thus conifers are 
 protected from disease in many cases by the copious flow of turpen- 
 tine, which forms an effectual barrier against the entrance of fungi as 
 well as bacteria. 5 The ethereal oils which are found so widely 
 distributed throughout the plant kingdom are known to possess 
 the ability of hindering, and in many cases actually destroying, 
 germs when brought in contact with them. 6 In all probability they 
 function in a similar way in the plant, although many parasites may 
 have adapted themselves to this condition. 
 
 1 Sternberg : Phil. Med. News, 1890, p. 262. 
 2 Nuttall: Boylston Essay, Harvard, 1888. 
 
 3 Fokker: Zeit. f. Hyg., IX (1890), 41. 
 
 4 Lehmann: Cent. f. Bakt. VII (1890), 457. 
 6 Hartig: Die Baumkrankheiten, S. 139, 166. 
 
 6 Cadeac et Meunier : Ann. de PInst. Past. 1889, 317. Freudenreich : Ann. de 
 Microg., 1889. 
 
Bacteria in their Relation to Vegetable Tissue. 31 
 
 Besides the possible sources of immunity and resistance which we 
 have already considered, we have the action of the living plasma of 
 the plant. Concerning the exact nature of this force we have but 
 little positive knowledge, although it is probably chemical in its 
 action. We know that the plant endowed with vital activity is more 
 resistant toward outside influences than the same dead structure; also, 
 that protoplasm which is in an active state is much less subject to 
 the attacks of disease than quiescent or inactive protoplasm. This 
 has been demonstrated in the case of a number of tree-destroying 
 fungi that are only able to overcome the tissue cells during the winter 
 season of rest. 1 Anything that tends to impair the normal exercise 
 of the vital functions of the protoplasm predisposes the plant to the 
 attack of outside organisms. It is quite unlikely that this so-called 
 lowering of the general vitality affects to any considerable extent the 
 physical means of resistance. It is much more probable that it is 
 the repelling ability of the living protoplasm that is weakened, and 
 thus less resistance is offered to disease. To this action Marshall 
 Ward attributes a large share of the resistance of the plant against its 
 parasitic foes. 
 
 Speaking of fungi, he says, so long as the protoplasm can over- 
 come, by respiratory oxidation or otherwise, the small amounts of 
 poison generated by the parasite, the hypha does not pass, but when 
 the poison exceeds this power of repulsion, then it effects an entrance 
 into the cell. 2 
 
 In here presenting the sources which seem to be operative in the 
 production of the resistance and immunity of plant-tissues, examples 
 have also been given illustrative of this condition with fungi as well 
 as bacteria. While the conditions necessary for the best develop- 
 ment of these two classes of vegetable life are often different, there 
 can be but little question that the same means of protection which 
 the plant possesses, operates in many cases against the one quite as 
 effectually as against the other. The refractoriness of higher plants 
 against bacteria has many more points in common with the same 
 phenomena against fungi, than it has with the action of the animal 
 body against bacterial life. 
 
 1 Hartig: Die Baumkrankheiten, S. 87, 112, 33 u. A. 
 
 2 H. Marshall Ward : Journ. Roy. Soc., 1890, 213. 
 
32 H. L. Russell. 
 
 CONCLUSIONS. 
 
 For sake of convenience, a short review of the points which have 
 been developed in the preceding pages will now be made. 
 
 1. The increasing importance of the bacterial portion of phyto- 
 pathology necessitates a more thorough investigation of the influence 
 of bacterial life in general upon plant-tissue than has heretofore been 
 considered necessary. 
 
 2. The artificial inoculation of higher plants with different micro- 
 organisms (not known to be pathogenic for plants) reveals the fact, 
 contrary to the usually accepted idea, that quite a goodly number of 
 different species are able to withstand the action of the living plant 
 organism for a not inconsiderable length of time. 
 
 3a. Of the species which are able to live in plant-tissues for a con- 
 siderable period of time, those which are ordinarily adapted to a 
 saprophytic method of existence are particularly prominent. Not 
 all saprophytes, however, possessed this power, but in certain forms, 
 as B. fluorescens, B. acid, lact., B. butyricus, etc., it was a marked 
 feature. 
 
 36. Among those forms which are facultative parasites upon the 
 animal body, but few were found that seemed to be able to live 
 in plant-tissue. With the exception of B. pyocyaneus and the 
 Schweineseuche bacillus, they gradually decreased in numbers and 
 finally died. 
 
 3c. The inoculation of plants, not taxonomically related to the 
 natural hosts of bacterial plant parasites, with species of micro- 
 organisms naturally parasitic on vegetable tissue, showed that while 
 the bacteria were unable to spread, they could survive at the inocu- 
 lation point in large numbers. 
 
 4. Not only were numbers of different species of bacteria able to 
 live in the plant from 40 to 80 days or more, but many of them 
 (mostly saprophytes) were able to spread throughout the tissue of the 
 plant to a limited extent (20 to 50 mm. or more). 
 
 5. The local distribution always took place in an upward direc- 
 tion, and the bacteria were found to be generally intracellular instead 
 of intercellular. 
 
 6. According to the present views of physiologists regarding the 
 transpiration stream, it does not seem possible that this current can 
 
Bacteria in their Relation to Vegetable Tissue. 33 
 
 account for the distribution of bacteria in the tissue. It seems to be 
 correlated much more closely with the actual growth of the micro- 
 organisms. 
 
 7. The facts already determined relative to the ability of sapro- 
 phytes to thrive in plant-tissues throw some light on the question 
 of the normal presence of bacteria in healthy plants. A large 
 number of cultures made from the inner tissue of healthy plant stems 
 revealed no bacteria, but where stems were wounded, even by a 
 needle-prick, the bacteria on the surface were able to enter and live 
 for a long time. Thus it is possible that bacteria may enter through 
 lesions so small as to escape notice, or they might even live in the 
 tissue after the wound had healed over. 
 
 8. With bacteria, not adapted for growth in plants, I have been 
 unable to prove that they could enter the plant where the epidermal 
 tissue was known to be intact. In the case of parasitic species on 
 plants, they sometimes effect an entrance into tissues without the 
 intervention of wounds of any sort. 
 
 9. The actual method by which saprophytes are able to spread in 
 plant tissues has not been satisfactorily determined, but it seems that 
 the cellulose wall undergoes a change that renders it permeable to 
 the bacteria. Those forms causing a pathological condition in the 
 plant spread, in many cases, by means of the fermentative and 
 destructive power they possess. 
 
 10. The phenomena, heretofore regarded as immunity of plants 
 from micro-organisms, present two phases so distinct in their action 
 that it seems proper to separate them to a certain degree. The 
 exemption of plants from bacteria in general is due to what may be 
 termed the resistance of the plant, while the more restricted term, 
 immunity, is reserved for the ability of a certain group of plants to 
 be refractory toward a disease germ that is able to cause a patho- 
 logical condition in closely allied forms of plant life. No hard and 
 fast limits can be drawn for the immunity of plants, as this condition 
 varies in each disease. The causes which bring about this ability of 
 the plant to repel not only bacteria in general, but those toward 
 which it is somewhat susceptible, are various. 
 
 In the case of immunity, physical causes, such as the epidermal 
 and cortical resistant tissues, matured and thickened cell walls of the 
 inner tissue, exclusion by gummy exudates, etc., are the leading 
 
34 H. L. Russell 
 
 factors. The exemption of plants from bacterial diseases, however, 
 does not rest upon any single factor but upon the interaction of 
 various causes. 
 
 Added to this mechanical source of immunity are the chemical 
 reaction of the juices, the unfavorable conditions of nutrition, the 
 action of the living protoplasm, etc., all of which exercise an unfa- 
 vorable or inhibitory effect on bacterial life. 
 
 The whole question of immunity of plants from bacteria is much 
 more closely related to the same question as regards fungi than it is 
 to the subject of immunity as seen in the animal kingdom. Vege- 
 table cell juices, aside from their acid reaction, are entirely powerless 
 against bacteria, and do not possess any germicidal properties like the 
 blood-serum of animals. 
 
 BIBLIOGRAPHY. 
 
 A. On the normal presence of bacteria in healthy tissue: 
 
 1. Bernheim : Munch, med. Wochen., 1888, s. 743. 
 
 2. Buchner: Munch, med. Wochen., 1888, No. 52. 
 
 3. de Vestea: Ann. de PInst. Pasteur, 1888, 670. 
 
 4. Fazio: Revista inter. d'Igiene, 1890. (Abs. : Cent. f. Bakt. 
 
 VII, 798.) 
 
 5. Fernbach : Ann. Past., 1888, 567. 
 
 6. Groucher et Deschamps: Arch. Med. Exp., 1889, 53. 
 
 7. Galippe: C. R. Soc. Biol., 1887, No. 25. 
 
 8. Laurent: Bull. PAcad. roy. de Belg., t. X, 38. 
 
 9. Laurent: Bull. PAcad. roy. de Belg., t. XIX (1890), 468. 
 
 10. Lehmann: Munch, med. Wochen., 1889, No. 7. 
 
 11. Ralph: Trans. Royal Soc. Victoria, Vol. XX, 1884. 
 
 12. Van Tieghem: Bull. Soc. Bot.de France, 1884, XXXI, 283. 
 
 B. On the artificial inoculation of plants with bacteria, non-parasitic in 
 
 vegetable tissue : 
 
 1. Lominsky : On the parasitism of some pathogenic microbes 
 
 for animals in living plants. Wratsch, 1890, No. 6. (Ref. 
 Cent. f. Bakt. VIII, 325.) 
 
 2. Savastano : Tuberculosi delP olivo : Ann. R. Scuola. Sup. 
 
 d'Agric. in Portici, Vol. V, 1887. 
 
Bacteria in their Relation to Vegetable Tissue. 35 
 
 APPENDIX GIVING A LIST OF THE BACTERIAL PLANT DISEASES, 
 WITH BRIEF KESUME OF THEIR PRINCIPAL CHARACTERISTICS. 
 
 The preparation of a complete abstract of the bacterial diseases of 
 plants at present is attended with some difficulty. Besides the num- 
 ber of well authenticated and confirmed observations upon this class 
 of diseases, there are quite a number of maladies which have been as 
 yet incompletely worked out. The disease has been experimentally 
 reproduced only by inoculation of diseased tissue, not by infection 
 from a pure culture of the germ. The classic canons of Koch, which 
 are regarded as essential in the elucidation of the etiology of an 
 animal disease, are, however, just as applicable in the investigation 
 of plant maladies, and we can consider no disease as sufficiently 
 proven to be of bacterial origin until the germ has first been isolated, 
 and then successful inoculation experiments made with the pure 
 culture of the organism. 
 
 The literature embracing this branch of phytopathology is largely 
 American, but it is widely scattered, and it was thought that a brief 
 resume of the bacterial plant-diseases known to date would be of 
 value. So far as I am aware, this has not yet been attempted in any 
 complete degree. Gomes' Crittogamia Agraria (Naples, 1891) and 
 Ludwig's Lehrbuch der Niederen Kryptogamen (Stuttgart, 1892) 
 are the only works from a European source that attempt to deal in 
 any satisfactory way with the bacterial plant-diseases, and even these 
 include only a part of the diseases already known. 
 
 Tables I and II give a list of those diseases which have been traced 
 to a bacterial origin and where the disease is claimed to have been 
 experimentally produced by inoculation of pure cultures. Table III 
 gives a provisional list of diseases possibly of bacterial origin, but 
 the etiology of each malady has not yet been traced to a specific 
 microbe, and consequently cannot be regarded as thoroughly proven. 
 
 The number of plant maladies caused by bacteria might have been 
 considerably increased if all the cases on record of the presence of 
 bacteria in diseased tissue had been added. This, however, does not 
 signify that the bacteria bear any etiological relation to the disease, 
 and it is possible that in many of these cases they are present only 
 as decomposition-organisms in dead or dying tissue. A considerable 
 number, however, of these have been added, as it has been suggested 
 that it might be useful to collect the data on this subject, imperfect 
 or otherwise, which at present are so , widely scattered in various 
 publications. 
 
TABLE I. BACTERIAL PLANT DISEASES. 
 
 SPECIFIC NAME OF 
 GERM. 
 
 Bac. amylovorus 
 (Burrill) De Toni. 
 
 Bac. sorghi, 
 Burrill. 
 
 NAME OF 
 DISEASE. 
 
 Pear blight. 
 Fire blight. 
 
 Sorghum 
 blight. 
 
 HOST PLANTS AFFECTED BY NATURAL AND 
 ARTIFICIAL INFECTION. 
 
 Pear (Pyrus communis). 
 
 Apple (P. malus). 
 
 Anier. mountain ash (P. Americana). 
 
 Crab-apple (P. sinensis). 
 
 Quince (Cydonia vulgaris). 
 
 English haw (Cratsegus oxyacantha). 
 
 " (C. tomentosa, var. parviflora). 
 Shadbush (Amelanchier Canadensis). 
 Red raspberry 1 (Turner and Marlboro var.) 
 Blackberry (var. Snyder). 
 Kelsey plum (Prunus sp. ) 
 
 l lu horizontal column refers to Detmer's work. 
 Actual inoculations in this case not made. 
 
 Sorghum vulgare. 
 
 #) saccharine var. 
 
 b) non " 
 S. halapense? 
 
 (broom corn). 
 
 ORGANS OF PLANT 
 AFFECTED. 
 
 Flower clusters, young 
 fruit, more succulent 
 woody tissue and foliage. 
 
 1 Base of stem and 
 branches. 
 
 Leaf-sheaths and leaves, 
 roots. 
 
 Bac. Zese, 
 Burrill. 
 (Bac. secales.) 
 
 Corn blight. 
 
 Zea mays. 
 
 Roots, stem (lower inter- 
 nodes), leaves and sheath, 
 fruit. 
 
 Bac. hyacinthi, 
 Wakker. 
 
 Yellows of 
 hyacinths. 
 
 Hyacinthus orientalis. 
 
 Xylem portion of fibro- 
 vascular bundle in bulbs 
 and leaves ; parenchyma 
 in leaves. 
 
 Bac. hyacinthi 
 septicus. 
 Heinz. 
 
 Hyacinth rot. 
 
 Hyacinthus sp, sp. Allium Cepa. 
 
 B. oleae-tuberculosis, 
 
 Savastano. 
 (B. oleas) Trev. 
 
 Tuberculosis. 
 
 (Rogna) 
 
 Italy. 
 
 (Maladie de 
 la loupe) 
 
 France. 
 
 Olea Europea. 
 
 Leaves, flower clusters, 
 and bulbs. 
 
 Cambium and bast of old 
 as well as young wood. 
 
MODE OP 
 NATURAL IN- 
 FECTION. 
 
 IMMUNE AND RESISTANT SPP. AS 
 
 TESTED BY ARTIFICIAL 
 
 INOCULATION. 
 
 GENERAL REMARKS. 
 
 BIBLIOGRAPHY. 
 
 Insects during 
 fertilization of 
 flower, punc- 
 ture by insect 
 stings, bites, 
 etc. 
 
 Cydonia Japonica, atomizing flowers. 
 
 Peach, nearly immune. (Arthur.) 
 
 Grape, 
 
 Mulberry, 
 
 Corn, 
 
 Potatoes, 
 
 Bean, 
 
 Onion, 
 
 Wheat and oats. 
 
 Natural immunity of diff. species of 
 pear family lost when subjected to 
 artificial inoculation. 
 
 A general infection usually 
 affecting the more succulent 
 parts of tree, recognized by 
 the blackened or burnt ap- 
 pearance (hence name fire 
 blight) of part affected, also 
 by gummy exudate. 
 
 Burrill : 3d 111. Rep. Agri. 
 1890. Amer. Nat. VII 
 (1883), 319. Trans. 111. 
 Hort. Soc. 1877, 1878. 111. 
 Indus. Univ. Rep. 1882. 
 
 Arthur : 4th, 5th and 6th 
 N. Y. Agri. Exp. Rep. 
 Proc. Acad. Sc. Phil. 1886. 
 Amer. Nat. XIX (1885), 
 1181. Proc. Amer. Ass. 
 Adv. Sc. 1885. Bot. Gaz- 
 ette X, 343. 
 
 Waite : Unpublished work 
 of U. S. Ag. Dept., Div. of 
 Veg. Path. 
 
 1 Detmers : Ohio Bull. No. 
 6, 1891. 
 
 Stomata and 
 roots. 
 
 Zea mays. 
 
 Triticum vulgare. 
 
 Sorghum vulgare (some varieties). 
 
 Some varieties of sugar sorghum 
 
 (Kellerman and Swingle). 
 
 Disease affects principally 
 leaves and their sheaths, also 
 the roots. Parts affected 
 show a crimson red patch, 
 usually circumscribed, not 
 causing a rupture on the sur- 
 face. Cell contents degen- 
 erate, walls turn red. 
 
 Burrill: 8th Rept. Soc. 
 Prom. Ag. Sc. 1887. Micro- 
 scope, Nov. 1887. 
 
 Kellerman and Swingle : 
 Kans. Rep. 1887 and 1888. 
 Bull. No. 5, Dec. 1888. 
 
 See J. of M. V. 195 for 
 discussion of a sorghum dis- 
 ease by Comes. 
 
 Artificial in- 
 oculation suc- 
 ceeded without 
 puncture. 
 
 Closely allied to sorghum 
 germ in appearance and by 
 its pathological changes in 
 tissue. Dark brown discolor- 
 ations on leaves. Where root 
 is affected whole plant suffers 
 in loss of nutrition. 
 
 Burrill: 3d. 111. Rep. 1890. 
 Am. Assoc. Ad. Sc. 1889. 
 Soc. Prom. Ag. Sc. 1889. 
 111. Bull. No. 6, 1889. 
 
 Duncanson : Nebr. Acad. 
 Sc. II. 
 
 All double red varieties and some other 
 double varieties immune under nat- 
 ural conditions, but lose immunity 
 when artificially infected. 
 
 Disease restricted in its 
 spread throughout tissue, 
 causing a degeneration of 
 primary cell wall and cell 
 contents, forming a gummy 
 exudate, yellow in color. 
 
 Wakker : Bot. Cent. XIV 
 (1883), 315. Arch, neer- 
 land. XXIII (1888), 1. 
 
 Disease pro- 
 duced arti- 
 ficially from 
 pure cultures. 
 
 From description of disease 
 and of germ, this disease 
 appears to be distinct from 
 Wakker's malady. Decom- 
 position of affected parts with 
 formation of foul-smelling 
 
 Heinz : Cent, f . Bakt. 1889, 
 Bd. IV, S. 535. 
 
 Growing point 
 (?) Savastano. 
 Stomata and 
 lenticels 
 (Prillieux.) 
 
 Peach, plum, apricot, grape, fig, pear, 
 apple, bitter orange, lemon, rose, and 
 several coniferous trees. 
 
 Bacteria cause destruction of 
 tissue and formation of spaces 
 in tissue. This induces sec- 
 ondary local growth and 
 causes an internal hypertro- 
 phy in bark which finally 
 produces local death of tissue. 
 
 Savastano: Ann. d. R. 
 Scuola Sup. d'Agric. in Por- 
 tici, Vol. V, fasc. IV, 1887. 
 
 Cavara : Monograph, 
 1889. 
 
 Prillieux : Monograph, 
 
 1890. C. R. Acad. CVII 
 249. 
 
 Pierce: Journ. of Myc. 
 
 1891, 140. 
 
38 
 
 H. L. Russell 
 
 
 TABLE II. BACTERIAL PLANT DISEASES. 
 
 SPECIFIC NAME OP 
 GERM. 
 
 NAME OF 
 DISEASE. 
 
 
 HOST PLANTS AFFECTED BY NATURAL AND 
 ARTIFICIAL INFECTION. 
 
 ORGANS OF PLANT 
 AFFECTED. 
 
 B. Veuillemini, 
 Trev. 
 (B. pini, Vuill.) 
 
 Tumors of 
 Aleppo pine. 
 
 Pinus halapensis. 
 
 Mature wood, especially 
 cambium and phloem. 
 
 Bacillus avenae, 
 Galloway. 
 
 Blight on oats. 
 
 Avena sativa. 
 
 Young plants (all parts). 
 
 Micrococcus of car- 
 nation blight 
 Arthur. 
 
 Carnation 
 blight. 
 
 Carnation pinks, other varieties of pinks. 
 
 Leaves. 
 
 Bacillus of surface 
 scab of potato 
 Bolley. 
 
 Superficial 
 potato scab. 
 
 Solanum tuberosum. 
 
 Tubers (only young), 
 locally in stems, young 
 sprouts and leaves. 
 
 Bact. of wet rot 
 Burrill. 
 
 Wet rot of 
 
 potato. 
 
 Potato (S. tuberosum). 
 
 Tubers, possibly leaves 
 and culms also. 
 
 Bac. of wet rot 
 Kramer. 
 
 Nassfaule. 
 (Wet rot.) 
 
 Potato. 
 
 Tubers. 
 
 Bacillus of beet-root 
 disease. 
 Arthur and Golden. 
 
 Sugar beet- 
 root disease. 
 
 Beta vulgaris (saccharine varieties). 
 
 Parenchyma of roots and 
 leaves, also fibre -vascular 
 tissue to less degree. 
 
Bacteria in thdr Relation to Vegetable Tissue. 
 
 39 
 
 MODE OF 
 NATURAL IN- 
 FECTION. 
 
 IMMUNE AND RESISTANT SPECIES AS 
 
 TESTED BY ARTIFICIAL 
 
 INOCULATION. 
 
 GENERAL REMARKS. 
 
 BIBLIOGRAPHY. 
 
 Insect wounds 
 (Vuillemin). 
 Stomata and 
 lenticels. 
 (Prillieux). 
 
 
 Closely allied to B. olese- 
 tuberc. Bacteria cause a 
 degeneration and partial de- 
 struction of tissue. This irri- 
 tation causes hypertrophy of 
 cambial and bast tissue which 
 produces an excrescence. 
 
 Prillieux : Monograph, 
 1890. Ref.: Zeit. f. Pflan- 
 zenkrank. I, 161. 
 Comes : Crittogamia 
 Agraria. 
 Vuillemin: C. R. Acad. 
 CVII (1888). 
 Bot. Zeit. 1889, 686. 
 
 Stomata (?). 
 Artificial in- 
 fection suc- 
 ceeds with 
 simple 
 spraying. 
 
 Triticum vulgare, 
 Zea mays, 
 Sorghum vulgare, 
 Hordeum vulgare, 
 Diff. spp. grasses. 
 
 Young plants (6-12 inches 
 high) are particularly sus-, 
 ceptible ; affects first the tips 
 of lower leaves, gradually 
 extending throughout the 
 whole plant. 
 
 Galloway: J. of M. VI 
 (1890). Bot. Gazette, XV, 
 228. Amer. Assoc. Aug. 
 1890. 
 
 Artificial in- 
 fection suc- 
 cessful upon 
 external ap- 
 plication. 
 
 
 Characteristics of disease ill- 
 defined, gradual dying of 
 leaves. Bacteria found abund- 
 antly in transparent spots on 
 leaves. 
 
 Arthur: A. A. A. S. Aug. 
 1890. Soc. Prom. Ag. Sc. 
 Ind. Exp. St. Bull. 1890. 
 
 Lenticels. 
 
 Aerial organs quite immune. 
 
 A disease favored by exces- 
 sive moisture, producing a 
 proliferation of lenticels, al- 
 lowing easier access of bac- 
 teria which produce a super- 
 ficial "scab." 
 
 Bolley: Ag. Sc. IV, Nos. 
 9 and 10. A. A. A. S. 
 (1890), 334-5. 
 
 
 
 A soft, wet rot emitting an 
 offensive odor germ, motile, 
 0.7x1. 1.5 n, non-liquefy- 
 ing bacillus. Proof of bacte- 
 rial cause not yet conclusive. 
 
 Burrill : Proc. Soc. Prom. 
 Ag. Sc. 1890, p. 21. 
 
 Lenticels or 
 wounds. 
 
 
 A liquefying butyric acid 
 producing bacillus. Infec- 
 tion experiments made only 
 with ripened tubers. 
 
 Kramer: Oest. land. Cent. 
 I, 11. Ref.: Cent. f. Bak. 
 X, 164. 
 
 Unknown. 
 
 
 Characters of disease in roots 
 not well defined ; leaves 
 puffed out in intervening 
 areas. Disease diminishes 
 the sugar contents of roots 
 to a considerable extent. 
 
 Arthur and Golden : 
 Ind. Bull. No. 39, Apr. 
 1892. Abst. in Exp. Stat. 
 Rec. Ill, No. 12. 
 
40 
 
 H. L. Russell. 
 
 TABLE III. PLANT DISEASES, PROBABLY OF BACTERIAL ORIGIN. 
 
 NAME OF 
 DISEASE. 
 
 HOST PLANTS 
 AFFECTED. 
 
 CHARACTERISTICS OF THE 
 DISEASE. 
 
 RESULTS OF ARTIFICIAL 
 INOCULATION. 
 
 BIBLIOGRAPHY. 
 
 Geranium 
 blight, 
 Bac. caulivor- 
 us.Pr.&Delx. 
 
 Pelargonium, diff. 
 spp. cult. 
 Geranium, cult. 
 Potatoes (stems). 
 
 A complete disorganiza- 
 tion of tissue of young 
 stems, especially "cut- 
 tings " of Geranium, which 
 manifests itself by a black- 
 ened shriveled appearance, 
 often extending to leaves. 
 
 Successful inoculation 
 made with diseased tissue 
 of Geranium in healthy 
 tissue of same plant ; also 
 infection of Geranium 
 from potato stems and vice 
 versa. (Prill, et Delx.) 
 
 Galloway, 
 Journ. of Myc. VI, 
 114. 
 Prillieux and Dela- 
 croix, 
 C. R. Acad. CXI, 
 208. 
 
 Cucumber rot. 
 Tomato blight. 
 
 Cucurbitaceous 
 plants like melons, 
 cucumbers, squash, 
 also tomatoes and 
 tubers of potatoes. 
 
 Disease marked by a very 
 rapid decay of the stem 
 and leaves as well as fruit. 
 In case of potatoes, the 
 aerial parts show a blight- 
 ed appearance, while the 
 tubers present a watery, 
 decayed mass. 
 
 Healthy plant stems, es- 
 pecially young succulent 
 ones, as well as fruit (to- 
 mato) were thoroughly 
 rotted by inoculation of 
 diseased tissue in short 
 time (6-24 hours). 
 * See note below. 
 
 Halsted, 
 Amer. Ass. Ad. Sc. 
 1891. Bull. No. 19, 
 Miss. Exp. Stat. 
 Jan. 1892. 
 
 Root rot of 
 vegetables. 
 
 Salsify, egg plant, 
 sweet potato, Irish 
 potato, onion, and 
 apple. 
 
 A slimy and very offen- 
 sive decomposition of root 
 crops beginning at lower 
 end and working its way 
 to the crown of plant. 
 
 Disease produced by trans- 
 fer of diseased tissue to 
 healthy plants. 
 
 Halsted, 
 Garden and Forest, 
 Nov. 26, '90. llth 
 N.J.Agr. Exp. Stat. 
 351. 
 
 Cabbage rot. 
 
 Cabbage, turnips. 
 
 General rot of cabbage 
 heads. 
 
 Positive results obtained 
 by inoculating diseased 
 tissue into healthy plants. 
 
 Gorman, 
 Amer. Assoc. Coll. 
 and Exp. Stat. 1891. 
 
 "Sereh" 
 disease. 
 
 Sugar cane (Java 
 and Sumatra). 
 
 Diseased plant has short 
 internodes, small leaves, 
 poorly developed root sys- 
 tem and a general appear- 
 ance of an insufficient 
 water supply. This is due 
 to the stoppage of ves- 
 sels by a gummy slime, 
 thought to be the product 
 of bacterial growth. 
 
 Two distinct spp. ob- 
 served by Janse, B. sac- 
 chari and B. glagae, but 
 no infection experiments 
 made with pure cultures. 
 Causal relation of bac- 
 teria to disease is not yet 
 thoroughly proven. 
 
 Janse : 
 Ref . in Cent, f . Bakt. 
 XI, 641. 
 Kruger : 
 Ber. d. Vers. Stat. 
 f. Zucker, 1890. 
 Benecke. 
 
 Certain "Gum" 
 diseases. 
 Bact. gummis, 
 Comes. 
 
 Various plants, 
 such as figs, grapes, 
 mulberry, to- 
 matoes, potatoes, 
 cabbage, beets, 
 carrots, etc. 
 
 Disease seems to affect 
 starch-bearing cells and 
 vessels. The starch is 
 decomposed and there is 
 formed a gummy sub- 
 stance that stops up the 
 vessels. Bacteria found 
 in abundance in this 
 gummy exudate. 
 
 In all probability there 
 are several distinct dis- 
 eases under this head. 
 Comes and Sorauer both 
 claim to have isolated 
 bacteria that were able 
 to set up this disturbance 
 in fresh, healthy tissue. 
 
 Sorauer : 
 Zts. f. Pflanzkrank. 
 11,280. 
 Comes: 
 Crittogam. Agraria. 
 
 * Cross inoculations, made between tomato, potato and melon from virus of one species on to the other, showed 
 
 that the rot was common to all. 
 
Bacteria in their Relation to Vegetable Tissw. 
 TABLE III. Continued. 
 
 41 
 
 NAME OF 
 DISEASE. 
 
 HOST PLANTS 
 AFFECTED. 
 
 CHARACTERISTICS OF THE 
 DISEASE. 
 
 RESULTS OF ARTIFICIAL 
 INOCULATION. 
 
 BIBLIOGRAPHY. 
 
 Celery blight. 
 
 Celery. 
 
 Affects leaves and their 
 stems, diseased tissue pre- 
 senting a watery appear- 
 ance. 
 
 Germ observed in tissue, 
 isolated and cultivated. 
 When introduced into 
 plant caused rapid decay. 
 
 Halsted: 
 N. J. Bull. Q. Apr. 
 21, '92. 
 
 White slimy 
 Flux, 
 Leuconostoc 
 Lagerheimii, 
 Ludw. 
 
 Oaks, poplars, 
 ash, willows. 
 
 Subcortical tissue. 
 
 Contagious disease dis- 
 seminated by insects and 
 caused by the symbiosis 
 of this germ with an en- 
 domyces and a yeast 
 fungus. 
 
 Ludwig : 
 Lehr. d. nied. Krypt. 
 1891. 
 
 Brown slimy 
 Flux, Microc. 
 dendroporthos, 
 Ludw. 
 
 Fruit trees, shade 
 trees, like elms, 
 poplars and 
 birches. 
 
 Affects wood and bark of 
 trees. Disease marked 
 by the exudation of a 
 yellowish brown slime 
 from wood layers which 
 ultimately destroys the 
 bark of tree. 
 
 Seems to be caused by a 
 germ which Ludwig has 
 named Mic. dendropor- 
 thos. Associated with 
 this is usually Torula 
 moniliodes, corda. 
 
 Ludwig : 
 Lehr. d. nied. Krypt. 
 '91. Also, Cent. f. 
 Bakt. 1891, 10. 
 
 
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