&V- 
 
 THE RESPIRATION OF CITRUS AS 
 
 AFFECTED BY HYDROCYANIC 
 
 ACID GAS FUMIGATION 
 
 BY 
 A. C. SHILL 
 
 University of California Publications in Agricultural Sciences 
 Volume 5, No. 5, pp. 167-180, 2 figures in text 
 
 1MVERSMY O* UttJKJKNi* 
 
 UBRAR 
 
 OOLLECE OF AGRICULTURE 
 DAVIS 
 
 UNIVERSITY OF CALIFORNIA PRESS 
 
 BERKELEY, CALIFORNIA 
 
 1931 
 
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THE RESPIRATION OF CITRUS AS 
 
 AFFECTED BY HYDROCYANIC 
 
 ACID GAS FUMIGATION 
 
 BY 
 A. C. SHILL 
 
University of California Publications in Agricultural Sciences 
 
 Volume 5, No. 5, pp. 167-180, 2 figures in text 
 
 Issued October 24, 1931 
 
 University of California Press 
 Berkeley, California 
 
 Cambridge University Press 
 London, England 
 
THE RESPIRATION OF CITRUS AS AFFECTED 
 
 BY HYDROCYANIC ACID GAS 
 
 FUMIGATION 
 
 BY 
 
 A. C. SHILL 
 
 INTRODUCTION 
 
 Hydrocyanic acid fumigation has been fairly widely used during 
 the past forty years or more for the control of various scale insects 
 attacking citrus. It has been the subject of much research but the 
 work done has been directed principally along such lines as insect 
 control and dosage application, the question of fundamental physio- 
 logical effects being largely neglected. 
 
 With citrus it has been learned that, in order to avoid damage 
 to the tree, such as scorching of foliage, certain conditions relating, 
 for instance, to light, heat, and humidity, must be fulfilled, but so 
 far as the writer is aware no more detailed knowledge of physiological 
 reactions is available. 
 
 The results of allied work, such as that dealing with hydrocyanic 
 acid fumigation of tomatoes and the effects of anaesthetics on plants, 
 while giving indications of what might be expected with citrus fumi- 
 gation, are apparently somewhat contradictory. It was therefore 
 decided to investigate to what extent, if any, the citrus tree reacts 
 to fumigation, using the respiration of the tree as an indication of 
 any effects taking place. 
 
 Summary of Literature 
 
 Moore (1916), investigating greenhouse fumigation with hydro- 
 cyanic acid, concluded that the gas enters through the stomata and 
 cuticle, the degree of entry depending on the thickness of the cuticle 
 and the amount to which it is cutinized. He also investigated the 
 effect of humidity and of temperature. Later, Willaman and Moore 
 (1917), using tomato plants, concluded that 
 
 a normal fumigation with hydrocyanic acid therefore results in a temporary de- 
 crease, followed by an increase in respiration [and that] plants subjected to 
 hydrocyanic acid fumigation absorb more or less of the gas, .... the immediate 
 
168 University of California Publications in Agricultural Sciences [Vol. 5 
 
 effect of the presence of this poison is a reduction in the activity of the oxidases 
 
 and catalases and hence in respiratory activity Within a few hours after 
 
 fumigation the oxidase activity has returned to normal, while the catalase and the 
 
 respiratory activities have exceeded the normal Eespiration remains above 
 
 the normal for several days. 
 
 Clayton (1919), also working with the tomato plant, found that 
 different concentrations of hydrocyanic acid gas gave effects ranging 
 from stimulative to depressive. The maximum of beneficial results, 
 as shown by growth measurements, etc., was secured from concentra- 
 tions deadly to insect life but just a little below the point of first 
 injury to the plant. 
 
 Osterhout (1918-19) concluded from a series of experiments using 
 different types of plants that anaesthetics, except in low concentra- 
 tions, produce a rise in respiration followed by a fall, the rise being 
 apparently associated with reversible anaesthesia and the fall below 
 normal indicating toxic effects, which result in a respiration decrease 
 much below normal. This is contrary to the theory of Verworn which 
 states that anaesthesia is a kind of asphyxia due to a checking of 
 respiration by the anaesthetic. Osterhout had previously shown 
 (1917) that, as regards permeability, there is a similarity in the 
 effects of potassium cyanide and of ether. 
 
 From work on Laminaria, Haas (1919) agreed with Osterhout 
 that anaesthetics produce an initial increase of respiration, followed 
 by a decrease if the anaesthetic is sufficiently toxic. Haas gives an 
 extensive review of the knowledge at that time of the effect of 
 anaesthetics and narcotics upon respiration, the results of various 
 workers being somewhat contradictory. 
 
 Recent work by Hanes and Barker (1931) on the effects of 
 hydrogen cyanide on the respiration of potato tubers has shown that 
 the respiration follows a two-phase course similar to that shown by 
 Osterhout, the changes in respiration being correlated with changes 
 in sugar concentration. 
 
 Medes and McClendon (1920) investigated the effect of anaesthetics 
 on Elodea : by measuring the consumption of oxygen they found that 
 the amount of oxygen used increased through the lower concentrations 
 of the anaesthetic, reached a maximum in the solution just failing 
 to cause permanent injury, and then decreased in those causing irre- 
 versible changes. 
 
 Cook (1925-26), using the phenolsulphonphthalein indicator 
 method as used by Osterhout, found that heavy metals caused the 
 respiration of Aspergillus to decrease from the first or to increase and 
 
1931] 
 
 SliiU: The Respiration of Citrus 
 
 169 
 
 subsequently diminish, and he also (1925-26o) investigated a latent 
 period occurring with the copper salts used. On the other hand 
 LeVan (1930) reports that salts of various metals stimulate the carbon 
 dioxide production of Lupinus alb us seedlings. 
 
 APPARATUS 
 
 After experimentation with various types of air pumps, gas absorb- 
 ers, and plant chambers, the apparatus diagrammatically represented 
 in figure 1 was evolved and used in this investigation. Slow steady 
 air circulation was obtained with a New Nelson pump geared down 
 
 Fig. 1. Diagram of apparatus used. 
 
 1. Trap. 2. 50% KOH absorbers. 3. Mercury manometer. 4. Bead tower 
 containing 36% H 2 SO, for humidity control. 5. Glass-wool air filter. 6. Bead 
 towers containing standard (N/10) KOH. 7. HON generator. 8. Water suction 
 pump. 9. Pot and citrus seedling. 10. Kespiration chamber and dark covering. 
 11. Supporting table with adjustable shelf. 
 
 to about one revolution per minute. The main set-up was connected 
 as a closed circuit during respiration determinations. The pump sup- 
 plied pressure and suction and the apparatus was arranged so that 
 the pressure was approximately atmospheric in the chamber. 
 
 The carbon dioxide was removed from the air before the air entered 
 the chamber and the humidity was regulated to approximately 65 per 
 cent, an average outdoor value. 
 
170 University of California Publications in Agricultural Sciences [Vol. 5 
 
 The carbon dioxide in the air leaving the chamber was absorbed 
 
 . . N 
 in Truog towers containing — KOH, and the air was then passed on 
 
 through the pump. The third Truog tower was needed only occa- 
 sionally as a check on absorption but it served to balance the pressure 
 on either side of the chamber. 
 
 The respiration chamber was an inverted 12-liter round-bottomed 
 flask darkened by being entirely covered with thick black paper or 
 rubberized aluminum-painted cloth. The pot containing the citrus 
 seedling to be tested rested on an adjustable shelf of the open-topped 
 supporting table, and the inverted flask was supported on a board 
 resting on the top of the table, having a central hole to accommodate 
 the neck of the flask. The leaves and branches of the potted tree 
 were "bunched up" by hand to get them inside the chamber and the 
 neck was then sealed with a split rubber stopper. The final sealing 
 of the neck was made with "Tree-Seal" (a proprietary product — ■ 
 asphalt water emulsion) and the chamber tested with a 10-cm. mercury 
 vacuum, which was a somewhat greater vacuum than that existing in 
 the chamber when carbon dioxide free air was rapidly passing through 
 from the line of potash absorbers. The asphalt emulsion was usually 
 sufficiently hardened after an hour, to make a perfect seal. 
 
 By including only the above-ground portion of the seedling in the 
 respiration chamber, blank tests to determine the carbon dioxide given 
 off by the soil, etc., were avoided, and the size of chamber was mini- 
 mized thereby facilitating the clearance of the air in the chamber. 
 
 Carbon dioxide free air could be passed rapidly through the 
 chamber by connecting to the water suction and to the line of 50 per 
 cent potash absorbers. 
 
 EXPERIMENTAL PROCEDURE 
 
 The plant to be tested was sealed in the chamber and then usually 
 left overnight, a constant stream of air being sucked through. Before 
 making a respiration determination this stream of air was increased 
 for some minutes and then a stream of carbon dioxide free air was 
 passed through rapidly for half an hour to remove any carbon dioxide 
 accumulation. 
 
 The chamber was then connected in the closed circuit for the 
 respiration determination, which took six hours. 
 
1931] Skill : The Respiration, of Citrus 171 
 
 The above procedure was followed for each determination, a stream 
 of air being sucked through the chamber continuously when a deter- 
 mination was not in progress. 
 
 When a fumigation was carried out, a rapid stream of air was 
 first sucked through the chamber. The charge of hydrocyanic acid 
 was then generated by adding a slight excess of sulphuric acid to a 
 weighed amount of sodium cyanide in the small generator and heating 
 it gently, the generator being connected to the chamber. Some 200 cc. 
 or so of air was then sucked through the generator in several portions, 
 thereby sweeping the gas into the chamber. A very small percentage 
 of the gas may have been removed from the chamber by this procedure 
 but this seemed to be the best method available with the small quan- 
 tities involved and with external generation. The gas was sealed in 
 the chamber for fifty minutes and then removed by a rapid stream 
 of air. 
 
 The Truog towers, to each of which was added at the start 50 cc. 
 
 N 
 of standard, approximately r^- KOH, were dismantled and washed 
 
 down with distilled water after each respiration determination. The 
 beads were then washed by decantation, transferred to a Buchner 
 funnel, and rewashed. The carbonate in the solution was precipitated 
 with excess neutral BaCl 2 solution, allowed to settle for half an hour, 
 and the excess alkali titrated slowly, without filtration, with standard 
 acid using phenolphthalein as indicator. 
 
 Carbon dioxide free water was not used in the determinations but 
 several "checks" were run with each series under the same conditions. 
 
 With regard to the air passing through the chamber it was verified 
 that the air entering was free of carbon dioxide. The clearance of 
 the air was reasonably satisfactory, for it was found by volume meas- 
 urements that a volume approximately twice that of the chamber 
 passed through in a six-hour run. Furthermore, in one experiment 
 when the respiration rate had become fairly steady the respiration 
 value for a fourteen-hour run was proportionately within 4 per cent 
 of the mean of the values for the preceding and the succeeding six- 
 hour runs. There was obviously a slight error owing to a higher con- 
 centration of carbon dioxide in the air in the chamber at the end than 
 at the beginning of each run of six hours, but the above figures 
 indicate that this was negligible. 
 
 The absorption of carbon dioxide from the air leaving the chamber 
 took place virtually entirely in the first Truog tower. The respira- 
 
172 University of California Publications in Agricultural Sciences [Vol. 5 
 
 tion values are given to the nearest milligram of carbon dioxide, the 
 accuracy of the method, as shown by analyses of "checks," etc., cor- 
 responding with this statement of results. The amounts of carbon 
 dioxide passed off were not reduced to standard leaf area since the 
 growth conditions of the plants varied. 
 
 Because of the balance of the apparatus, the pressure in the 
 chamber was approximately atmospheric throughout [± 5 mm. mer- 
 cury pressure]. The temperature of the room was so regulated that 
 during a series of determinations on one plant it was within a maxi- 
 mum range of 4° C, the variation for any determination being not 
 more than 2° C. 
 
 HYDROCYANIC ACID DOSAGE 
 
 In citrus fumigation the average 100 per cent field dosage is 20 cc. 
 of liquid IICN or 1 oz. NaCN with H 2 S0 4 ) per 100 cu. ft. 
 
 Knight (1925) showed that in a tight fumigatorium of 100 cu. ft. 
 capacity 100 per cent dosage (20 cc.) killed all beetles and scales in 
 20 minutes, and 50 per cent dosage (10 cc.) killed all beetles and 
 scales in 40 minutes, this latter dosage giving 0.23 per cent HON in 
 the container. His results show that 25 to 50 per cent field dosage 
 in an air-tight chamber approximates 100 per cent dosage under field 
 conditions where a tent is used. 
 
 It was decided to use in these experiments a dosage of 75 per cent 
 of the 50 per cent field dosage in order to approximate field condi- 
 tions. Occasional slight burning of the young leaves indicated that 
 this was probably a comparative dosage. 
 
 Using the formula quoted by Hume (1926), for the chamber used 
 (volume 11.8 liters) the quantities were 0.044 grs. NaCN and 0.16 cc. 
 of dilute acid (approximately 10 cc. concentrated ILS0 4 to 13 cc. 
 water ) . 
 
 This dosage was used in all the experiments but one, in which the 
 dosage was doubled. 
 
1931] Shill: The Respiration of Citrus 173 
 
 EXPERIMENTAL RESULTS 
 
 The results obtained with various potted trees are tabulated and 
 graphically represented (ef. tables 1 and 2, fig. 2) and need little 
 explanation. 
 
 The first experiment (cf. table 1) showed an immediate stimulative 
 effect on the respiration following the fumigation. This was verified 
 with the next seedling and a decrease in respiration shown to follow 
 the initial stimulation. In the third experiment the main purpose 
 was to verify the later behavior, and with only one reading soon after 
 fumigation the maximum of the stimulative effect is not so well 
 defined. 
 
 The above-mentioned experiments were carried out at Berkeley. 
 Later, after setting up a similar apparatus at Riverside, it was decided 
 to try to ascertain more definitely whether the respiration after the 
 initial stimulation fell below the normal value. Respiration deter- 
 minations were therefore made for several days before fumigation 
 (cf. table 2), and it was found that after a rapid decrease at first, 
 the respiration curve flattened out, presumably after the quickly 
 available reserves were utilized, thereby making it possible to predict 
 what would be the approximate respiration values on succeeding 
 days without fumigation. The next two experiments, Nos. 4 and 5 
 (table 2) were carried out in this manner. In one case (No. 4) the 
 plant was fumigated again some two hundred hours after the first 
 fumigation, and it is seen (No. 4) that the plant gave a similar 
 reaction but to a lesser degree, the smaller reaction being due doubtless 
 to depleted reserves. In one case the respiration subsequent to fumi- 
 gation was slightly greater than the probable value without fumigation 
 and in the other case it was slightly less. The respiration after fumi- 
 gation in the second and third experiments apparently also decreased 
 to an approximate untreated value, allowing for an initial sharp 
 decrease followed by a gradual decrease if untreated, as indicated in 
 the fourth and fifth experiments. 
 
 In the last experiment (No. 6) a seedling was fumigated with a 
 dosage twice that used in the previous cases. While (cf. No. 5) the 
 stimulation in this case was not noticeably different from those having 
 the normal dosage, the subsequent respiration fell somewhat below 
 the probable value without fumigation. 
 
ioc so o 
 
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 Hours after fumigation. 
 
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 1. Mean time of each six hours determination plotted. 2. X, Y, and Z are 
 the approximate "untreated" curves, for comparison. 3. Fumigation dosage 
 with No. 6 twice that used with Nos. 2, 3, 4, and 5, the latter dosage approxi- 
 mating to 100% field dosage. 
 
1931] 
 
 SUM: The Respiration of Citrus 
 
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 Skill: The Respiration of Citrus 
 
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178 University of California Publications in- Agricultural Sciences [Vol. 5 
 
 The plant used for the second experiment was tested, without 
 fumigation, after it had been returned to the greenhouse for a month. 
 Over a period of five days it gave low and practically constant read- 
 ings, this being probably due to the fact that it was still suffering 
 from depletion of reserves after being kept in the dark for the fumi- 
 gation experiment, the winter weather at Berkeley not aiding a quick 
 recovery. 
 
 DISCUSSION 
 
 A general consideration of the foregoing results shows that, with 
 citrus, fumigation with a dosage of hydrocyanic acid approximating 
 that in field use for scale insect control produces an increase in 
 respiration, which, within the limits of accuracy of the determinations, 
 seems to reach a maximum about ten hours after fumigation. The 
 respiration returns to approximately a normal value some thirty-five 
 hours after fumigation. The fact that the rate of respiration, except- 
 ing the initial increase, associated by Osterhout (1918-19) with 
 reversible anaesthesia, apparently does not fall below the normal value, 
 indicates that this dosage has no appreciable, if any, toxic effect on the 
 tree. The one test carried out with twice the normal dosage indicated 
 a toxic effect. 
 
 The above findings are in accord with those of Osterhout (1918- 
 19) and his coworkers relating to the effects of anaesthetics upon the 
 respiration of various plants, including bacteria, higher fungi, algae, 
 and flowering plants, and with those of Hanes and Barker (1931). 
 They do not, however, parallel the conclusions of Moore and Willaman 
 (1917), who, working with hydrocyanic acid fumigation of tomatoes, 
 found a reverse effect, namely a decrease in respiration followed by 
 an increase above the normal, the latter effect lasting for several days. 
 The results obtained with citrus make it seem doubtful whether the 
 stimulative and beneficial results obtained by Clayton (1919) with 
 tomatoes, with concentrations deadly to insect life but just below the 
 point of first injury to the plant, exist with citrus fumigation, at least 
 to any extent. 
 
 It may be that with citrus, there is an initial decrease in respira- 
 tion immediately following fumigation, not evident with the time- 
 period used in the determinations, but the agreement with Osterhout 's 
 findings renders this unlikely. 
 
 From a practical standpoint, it is necessary to know the relative 
 effects of various control measures on the tree as well as their effects 
 
1931] Skill: The Respiration of Citrus 179 
 
 on an insect, and while work such as that of Knight, Chamberlain, and 
 Samuels (1929) has served to give an indication of the effects on the 
 tree, of oil sprays, the other principal method of citrus scale insect 
 control, this investigation serves to yield somewhat similar informa- 
 tion relative to fumigation. Further work along similar lines would 
 doubtless help to elucidate the effects of various fumigation factors 
 such as temperature and humidity. 
 
 ACKNOWLEDGMENTS 
 
 This work was carried out as part-time study while the author was 
 holding a Colonial Agricultural Scholarship (British Government) at 
 the University of California and he herewith expresses his thanks for 
 the assistance of both the Government and the University. 
 
 He also wishes to thank Dr. S. H. Cameron, of the University at 
 Berkeley, for his help when commencing the investigation, and Dr. 
 H. S. Reed and various members of the staff of the Citrus Experiment 
 Station at Riverside, for their criticisms. 
 
 SUMMARY 
 
 1. The fumigation of citrus with a dosage of hydrocyanic acid 
 approximating that used in the field produces an initial increase in 
 respiration (averaging about 75 per cent), followed by a return to an 
 approximate normal value after about thirty-five hours, the respiration 
 throughout being under conditions prohibiting photosynthesis. 
 
 2. Since the subsequent respiration does not markedly decrease 
 below the normal value it seems that with the dosage used in the 
 field there is no permanent toxic effect on the trees. Higher dosage 
 indicates a toxicity. 
 
180 University of California Publications in Agricultural Sciences [Vol. 5 
 
 LITERATURE CITED 
 
 Clayton, E. E. 
 
 1919. Hydrogen cyanide fumigation. Bot. Gaz., 67:483-500. 
 
 Cook, S. F. 
 
 1925-26. The effects of certain heavy metals on respiration. Jour. Gen. 
 
 Phys., 9:575-601. 
 1925-26«. A latent period in the action of copper on respiration. Jour. Gen. 
 
 Phys., 9:631-650. 
 
 Haas, A. R. C. 
 
 1919. Effect of anesthetics upon respiration. Bot. Gaz., 67:377-404. 
 
 Hanes, C. S., and Barker, J. 
 
 1931. The physiological action of cyanide. 1. The effects of cyanide on the 
 respiration and sugar content of the potato at 15° C. Proc. Eoy. 
 Soc, ser. B, 108:95-118. 
 Hume, H. H. 
 
 1926. The cultivation of citrus fruits (New York), p. 527. 
 
 Knight, H. 
 
 1925. Factors affecting efficiency in fumigation with hydrocyanic acid. Hil- 
 gardia, 1:35-56. 
 
 Knight, H., Chamberlain, J. C, and Samuels, C. D. 
 
 1929. On some limiting factors in the use of saturated petroleum oils as in- 
 
 secticides. Plant Phys., 4:299-321. 
 
 LeVan, W. C. 
 
 1930. The effect of metals on the respiration of Lupinus albus. Am. Jour. 
 
 Bot., 17:381-395. 
 
 Medes, G., and McClendon, J. F. 
 
 1920. Effects of anesthetics on various cell activities. Jour. Biol. Chem., 
 
 42:541-568. 
 Moore, W. 
 
 1916. Studies in greenhouse fumigation with hydrocyanic acid. Report State 
 
 Entomologist, Minn. (1915-16), pp. 93-108. 
 
 Moore, W., and Wlllaman, J. J. 
 
 1917. Studies in greenhouse fumigation with hydrocyanic acid: physiological 
 
 effects on the plant. Jour. Agr. Res., 11:319-338. 
 
 Osterhout, W. J. V. 
 
 1917. Similarity in the effects of potassium cyanide and of ether. Bot. Gaz., 
 
 63:77-80. 
 1918-19. Comparative studies on respiration. Jour. Gen. Phys., 1:171-179. 
 
UNTVERSITY OF CALD?OBNIA PUBLICATIONS— (Continued) 
 
 8. Microsporogenesis of Ginkgo blloba L. with, especial reference to the 
 
 Distribution of the Plastids and to Cell Wall Formation, by Margaret 
 Campbell Mann. Pp. 243-248, plate 52. September, 1924 ._ .26 
 
 9. Inheritance in Crepis capillaris (L.) Wallr. in. Nineteen Morphological 
 
 and Three Physiological Characters, by J. L. Collins. Pp. 249-296, 
 plates 45-52. December, 1924..! .75 
 
 10. Chromosome Number and Individuality in the Genus Crepis. L A Com- 
 
 parative Study of the Chromosome Number and Dimensions of Nineteen 
 Species, by Margaret Campbell Mann, Pp. 297-314, plate 53. March, 
 1925 .30 
 
 11. Chromosome Number and Individuality in the Genus Crepis. IL The 
 
 Chromosomes and Taxonomic Relationships, by Ernest Brown Babcock 
 
 and Margaret Mann Lesley. Pp. 315-341, 7 figures in text. March, 1926. .45 
 
 12. Chromosomal Chimeras in Crepis, by Lillian Hollingshead. Pp. 343-354, 
 
 plates 54, 55, 2 figures in text. March, 1928 _ _... .25 
 
 IS. Chromosome Numbers and Morphology in Trifolium, by Haakon Wexelsen. 
 
 Pp. 355-376, 4 figures in text. May, 1928 _ _ .25 
 
 14. Studies on Polyploidy. I. Cytological Investigations on Triploidy in 
 
 Crepis, by M. Navashin. Pp. 377-400, plates 56, 57. March 1929 .30 
 
 15. Meiosis in Two Species and Three Hybrids of Crepis and Its Bearing on 
 
 Taxonomic Relationship, by E. B. Babcock and J. Clausen. Pp. 401- 
 
 432, plates 58-61, 1 figure in text. May, 1929 40 
 
 Index, pp. 433-438. 
 
 VoL 3. L New Grasses for California. L Phalaris stenoptera Hack., by P. B. 
 
 Kennedy. Pp. 1-24, plates 1-8. July, 1917 _ _ _ SO 
 
 2. Optimum Moisture Conditions for Young Lemon Trees on a Loam Soil, by 
 
 L. W. Fowler and C. B. Lipman. Pp. 25-36, plates 9-1L September, 1917. J.5 
 S. Some Abnormal Water Relations in Citrus Trees of the Arid Southwest 
 
 and Their Possible Significance, by Robert W. Hodgson. Pp. 37-54, plate 
 
 12. September, 1917 „ _ '. „ 20 
 
 4. A New Dendrometer, by Donald Bruce. Pp. 55-61. November, 1917 .10 
 
 5. Toxic and Antagonistic Effects of Salts on Wine Yeast (Saccharomyces 
 
 ellipsoideus), by S. K. Mitra. Pp. 63-102. November, 1917 .45 
 
 6. Changes in the Chemical Composition of Grapes during Ripening, by F. T. 
 
 Bioletti, W. V. Cruess, and H. Davi. Pp. 103-130. March, 1918 25 
 
 7. A New Method of Extracting the Soil Solution (a Preliminary Communi- 
 
 cation), by Charles B. Lipman. Pp. 131-134. March, 1918 .05 
 
 8. The Chemical Composition of the Plant as Further Proof of the Close 
 
 Relation between Antagonism and Cell Permeability, by Dean David 
 Waynick. Pp. 135-242, plates 13-24. June, 1918 _ 1.25 
 
 9. Variability in Soils and Its Significance to Past and Future Soil Investi- 
 
 gations. I. A Statistical Study of Nitrification in Soil, by Dean David 
 Waynick. Pp. 243-270, 2 figures in text. June, 1918 „ „ .30 
 
 10. Does CaCo, or CaSo, Treatment Affect the Solubility of the Soil's Con- 
 
 stituents?, by C. B. Lipman and W. F. Gericke, Pp. 271-282. June, 1918 .10 
 
 11. An Investigation of the Abnormal Shedding of Young Fruits of the Wash- 
 
 ington Navel Orange, by J. Eliot Coit and Robert W. Hodgson. Pp. 
 283-368, plates 25-42, 9 figures in text. April, 1919 _ 1.00 
 
 12. Are Soils Mapped under a Given Type Name by the Bureau of Soils Method 
 
 Closely Similar to One Another?, by Robert Larimore Pendleton. Pp. 
 
 369-498, plates 43-74, 33 figures in text. June, 1919 .„ _. 2.00 
 
 Index, pp. 499-506. 
 
 VoL 4. 1. The Fermentation Organisms of California Grapes, by W. V. Cruess. Pp. 
 
 1-66, plates 1-2, 15 figures in text. December, 1918 „ .75 
 
 2. Tests of Chemical Means for the Control of Weeds. Report of Progress, 
 
 by George P. Gray. Pp. 67-97, 11 figures in text _„ _ „ .30 
 
 3. On the Existence of a Growth-Inhibiting Substance in the Chinese Lemon, 
 
 by H. S. Reed and F. F. Halma. Pp. 99-112, plates 3-8. February, 1919. .25 
 
 4. Further Studies on the Distribution and Activities of Certain Groups of 
 
 Bacteria in California Soil Columns by Charles B. Lipman. Pp. 113-120. 
 April, 1919 ..„ „ „ .10 
 
 5. Variability in Soils and Its Significance to Past and Future Soil Investi- 
 
 gations, n. Variations in Nitrogen and Carbon in Field Soils and Their 
 Relation to the Accuracy of Field Trials, by D. D. Waynick and L. T. 
 Sharp. Pp. 121-139, 1 figure in text. May, 1919 „ - _ „ 20 
 
UNIVERSITY OF CALIFORNIA PUBLICATIONS— (Continued) 
 
 6. The Effect of Several Types of Irrigation Water on the pH Value and 
 
 Freezing Point Depression of Various Types of Soils, by D. R Hoagiand 
 
 and A. W. Christie. Pp. 141-167. November, 1919 _ .25 
 
 7. A New and Simplified Method for the Statistical Interpretation of Bio- 
 
 metrical Data, by George A. Linhart. Pp. 159-181, 12 figures in text. Sep- 
 tember, 1920 _ _ .26 
 
 8. The Temperature Relations of Growth in Certain Parasitic Fungi, by 
 
 Howard S. Fawcett. Pp. 183-232, 11 figures in text. March, 1921 .75 
 
 9. The Alinement Chart Method of Preparing Tree Volume Tables, by Donald 
 
 Bruce. Pp. 233-243. December, 1921 _ _ _ _ .20 
 
 10. Equilibrium Studies with Certain Acids and Minerals and their Probable 
 
 Relation to the Decomposition of Minerals by Bacteria, by Douglas 
 Wright, Jr. Pp. 245-337, 35 text figures. March, 1922 _ 1.25 
 
 11. Studies on a Drained Marsh Soil Unproductive for Peas, by Paul S. 
 
 Burgess. Pp. 339-396, 21 figures in text. June, 1922 _ __ .65 
 
 12. The Effect of Reaction on the Fixation of Nitrogen by Azotobacter, by 
 
 Harlan W. Johnson and Charles B. Lipman. Pp. 397-405, 3 figures in 
 text. December, 1922 „ „ _ _ .25 
 
 IS. The Toxicity of Copper Sulfate to the Spores of Tilletia tritlci (Bjerk.) 
 Winter, by Fred N. Briggs. Pp. 407-412, 1 figure in text. November, 
 1923 _ _ „ „ _.... .25 
 
 14. Influence of Reaction on Inter-Relations Between the Plant and its Culture 
 
 Medium, by J. J. Theron. Pp. 413-444, 12 figures in text. January, 1924 .45 
 Index, pp. 445-450. 
 
 VoL 5. L Growth and Differentiation in Apricot Trees, by H. S. Reed. Pp. 1-55, 
 
 18 figures in text. September, 1924 .76 
 
 2. Studies Concerning the Essential Nature of Aluminum and Silicon for 
 
 Plant Growth, by Anna L. Sommer. Pp. 57-81, 2 figs, in text. May, 
 1926 _„ _ _ _ .30 
 
 3. The Growth of Citrus Seedlings as Influenced by Environmental Factors, 
 
 by Raymond E. Girton. Pp. 83-117, 8 figures in text. April, 1927 .45 
 
 4. Studies of Sulfur in Relation to the Soil Solution, by Wilbur L. Powers. 
 
 Pp. 119-166, 13 figures in text. December, 1927 .60 
 
 5. The Respiration of Citrus as Affected by Hydrocyanic Acid Gas Fumiga- 
 
 tion, by A. C. Shill. Pp. 167-180, 2 figures in text. October 1931 25 
 
 Vol. 6. 1. Chromosomes and Phylogeny in Crepis, by Lillian Hollingshead and Ernest 
 
 B. Babcock. Pp. 1-53, 24 figures in text. January 1930 _ _ 65 
 
 2. Cytological Investigations of Hybrids and Hybrid Derivatives of Crepis 
 
 capillaris and Crepis tectorum, by Lillian Hollingshead. Pp. 65-94, 
 plates 1-3, 19 figs, in text. January 1930 „ .50 
 
 3. Unbalanced Somatic Chromosomal Variation in Crepis, by M. Navashin. 
 
 Pp. 95-106, plates 4, 5, 2 figures in text. March 1930 .._ 25 
 
 4. A Cytological Study of Haploid Crepis Capillaris Plants, by Lillian Hol- 
 
 lingshead. Pp. 107-134, plates 6-8, 13 figures in text. November 1930 35 
 
 5. Cytological Studies of Five Interspecific Hybrids of Crepis Leontodon- 
 
 toides, by Priscilla Avery. Pp. 135-167, 18 figures in text. December 
 1930 - 45 
 
 6. The Lnterspeciflc Hybrid, Crepis rubra x C. f oetida, and Some of its Deriva- 
 
 tives. I, by Charles F. Poole. Pp. 169-200, plates 9-1L 7 figures in text. 
 March 1931 - 40 
 
 7. Spontaneous Chromosome Alterations in Crepis Tectorum L., by M. Nava- 
 
 shin. Pp. 201-206, 1 figure in text. April 1931. 
 
 8. Chromatin Mass and Cell Volume in Related Species, by M Navashin. 
 
 Pp. 207-230, 3 figures in text. April 1931. 
 
 Nos 7 and 8 in one cover - -40 
 
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 address the Agricultural Experiment Station, Berkeley, California. 
 
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