&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 UNIVERSITY OF CALIFORNIA PUBLICATIONS Note. — The University of California Publications are offered in exchange for the publi- cations of learned societies and institutions, universities and libraries. Complete lists of ail the publications of the University will be sent upon request. For sample copies, lists of publications, and other information, address the MANAGER OF THE UNIVERSITY PRESS, BERKELEY, CALIFORNIA, U.S.A. All matter sent in exchange should be addressed to THE EXCHANGE DEPARTMENT, UNIVERSITY LIBRARY, BERBELEY, CALIFORNIA, U. S. A. Publications of the University of California Press may also be obtained from THE CAMBRIDGE UNIVERSITY PRESS, FETTER LANE, LONDON, B.C. 4, England, to Which orders originating In Great Britain and Ireland should be sent. AGRICULTURAL SCIENCES. — O. B. Llpman, H. S. Reed, R. E. Clausen, Editors. Price per volume, $5. Volumes 1, 2, 3, and 4 completed. Volumes 5 and 6 in progress. VoL L 1. The Distribution and Activities of Bacteria in Soils of the Arid Region, by Charles B. Llpman. Pp. 1-2L October, 1912 $0.20 2. Studies on the Phenoldlsulphonic Acid Method for Determining Nitrates in Soils, by 0. B. Llpman and L T. Sharp. Pp. 23-37. October, 1912 .15 S. The Effects of Calcium and Magnesium Carbonates on Some Biological Transformations of Nitrogen in Soils, by W. P. Kelley. Pp. 39-49. December, 1912 _ 10 4. The Aluminum Reduction Method as Applied to the Determination of Nitrates in "Alkali" Soils, by Paul S. Burgess. Pp. 51-62. May, 1913 .15 5. 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Certain Effects under Irrigation of Copper Compounds upon Crops, by R. H. Forbes. Pp. 395-496, plates 16-19. March, 1917 _ 1.00 13. Experiments on the Effects of Constituents of Solid Smelter Wastes on Barley Growth in Pot Cultures, by C. B. Llpman and W. F. Gericke. Pp. 495-587. March, 1917 _ _ - - — .95 Index, pp. 589-^595. VoL 2. L Studies In Juglans. L Study of a New Form of Juglans californica Wat- son, by Ernest B. Babcock. Pp. 1-46, plates 1-12. December, 1913 .60 2. Studies in Juglans. II. Further Observations on a New Variety of Juglans californica Watson and on Certain Supposed Walnut-Oak Hybrids, by Ernest B. Babcock. Pp. 47-70, plates 13-19. October, 1914 M 3. Studies in Juglans. m. (1) Further Evidence that the Oak-like Walnut Originates by Mutation; (2) A Parallel Mutation in Juglans hlndsil (Jepson) Sargent, by Ernest B. Babcock. Pp. 71-80, plates 20-21. Sep- tember, 1916 .10 4. Mutation in Matthiola, by Howard B. Frost. Pp. 81-190, plates 22-36 November, 1919 ■ UBO 6. Interspecific Hybrids In Crepis. I. Crepis capillarls (L) Wallr. X 0. tec- torum L., by Ernest B. Babcock and Julius L. Collins. Pp. 191-204, plates 36-38. October, 1920 _ _ .20 6. Lrheritance in Crepis capillarls (L.) Wallr. L Inbreeding and Cross-breed- ing In Crepis capillarls (L.) Wallr., by Julius L. Collins. Pp. 205-216, plates 39-41. November, 1920 .30 7. Doheritance in Crepis capillaris (L.) Wallr. n. Lrheritance of Some Mor- phological Characters in Crepis capillarls, by Venkata Rau. Pp. 217-242, plates 42-43, 3 figures In text. June, 192S _ .35 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 Hours before fumigation 100 150 200 Hours after fumigation. 30 \ l\ M&BS X5 \ ' \ co 2 \ ' \ ?E"R & 20 HOURS V i \ V — — — 2 15 10 s FUMIGATION t No£N^ ioo so Hours before fumigation. < Fig. 50 100 150 Hours after fumigation. 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 175 W i-Q PQ < B W 3 a a PQ X t-l '■SO 2 2o g t^ O l-~ O CN OS CO i-H t^ 00 •* CI 00 1^ 'Ec'-a *-* CO rt co co IM rt ^ 1-1 (M ^ S E<° P5 5P s 3 3 c c 3 3 a 3 3 O O S O c £ _o 3 c •- CO £§ ■s's .0 c od +3 cS a — - o3 4^ 03 CO bJD a bD a .0 cj ho a bC bO a'a 3 ,3 !- i* 03 03 bC 1 03 a 03 a 03 bJD 1 tH 03 bC 53 bu 'g z I co bC 03 O u t_! 3 -*J 43 -fJ •+J +3 03 ■+-> to s 3 5 » CT3 CD c3 03 at 03 cS 03 CD t — "S si 03 0> "S [h 03 03 CO 03 03 01 t- Cj 03 03 03 H u U t. t. — ■~ Ut O 03 — Lh 03 03 03 03 O O C c 03 — 5 3 O .3 -3 .3 CO — CX) CO 03 c — 00 C3 E-4 3 tH CM re *^ 02 t^ CN •* CO 3 b- O O O O O c O O .3 O _a *» +J -w -^ -t-2 .3 -*- 1 -4-* -m -^" -*^ co y-l 00 1- IO <M O CO T— ( CM ^H co CO 1-1 1-1 N "* O 71 ■«*< CO B3 S3 O O O u C ga O £35 3 1, <M (N 1— 1 -*^ a> a « fc- C3 1 1 1 §73 B c t^ to lO rH 1— < »— < Ha T3 h J3 ■si O O co C5 03 O CO C5 03 g3« 05 O 1—1 O C «5 CD _2 00' 03 of 01 03 §|.s Eh 73 3 t-l 93 3 Ui » a e Z 3 03 a 03 9 "J -^ bC 03 Q s 03 -^ be 03 a 03 13 03 1-. z - SI > £ > O O '2 CO a £ 1 3 £ I .2 Q 1 3 rt* v -; >< *" 2 10 10 e« g t-H i-H »*- I> a t^ C5 c3 . rs &> CT (-3 B c3 -f3 03 O bC 03 03 03 _=: C bO be -tJ bit > "*f t3 fcn 3 t* 3 03 a c Z d 3 o3 03 03 B O tH O tH [S fc* CO CO CO O CO C 03 3 4) (-. 3 0^ .5-5 i—( <N CO 'E S - - H 176 University of California Publications in Agricultural Sciences [Vol. 5 is I ^lOO>OOt^<COcM^©Ci OOi— i00«om©C5C»5CM©iOSO5O S-3 C o s — o o o 'a "a _ 3 3 CO -^ -fc3 -tJ If <*- 3 y3 M [ft ffi 5 sp-g a a 1*2 (CtCC -w CO «- . o o o 2 CO CO CO CO "3 "3 O 3 3 3 CO o o O O o 3 5 5 J %* S ^ n ° o o +j *» ^ M h CO Ol o o .2 1 ""S •g MM .sp a a "" B g to c2 <c • tS ^ ** 2 a *s c fl c .2 .2 .2 •4^ -4^> +i d oi d h£> Mi hJ3 a "a a 3 3 C C g o §1 -+j -^ -*^> -+j M3 M 03 03 bp fat a s 3 * a a a - .SP SP E 3 *» tE •—■ C. £ (h S jj CU _CJ 0> v- <— CO 50 3 3 P 2 J3 J .SP"2 12 "§ o£°°0)O*a)» 3. O O O _2 — — -O. *-« .^ pi *> - o _C O <M NO e«5 i-h '-' « ° ° ■** Tj< O N H 00 CO 7-1 >-l 3 u u a ^ CU CD OJ c3 cs CO CO 3 M o o o t^ t^ CM 00 o o _c -3 C3 oS CO 02 3. - 3 3 CM CM CM CM C5 CO i< rn i-i o o +^> -1^> rH 00 - CD CM CO t~- —I H a 5 re H »> CM (2 « £ H g 5 <4 S Sou a o.2 r! ^ ,- ■ c -°s -a £-3 111 a *£ & -^ -CO o o CM O O o o —i 4> S £ b 1 cu T i-H O o - bfl 2 l .3 CM — c I- cu cu c ca O 0) -w M cu c 9 3 cc O 1931] Skill: The Respiration of Citrus 177 o 00 c t~ ce o CO CI CO re CN i — i 03 o is -w s — ** a a o c c 3 a 3 a 3 z 03 o3 o3 o _o z _o _o "S tr +a a3 fat be i[ 03 03 r. 03 o3 be a | E <v a 3 M -1. bC bC Si a bC 03 CO S 3 3 £ a 3 0! o CD »^ CU u. o — s-. Jh s-< a; ij O 1 — _ ~ o> CD CU a> <u c3 CD o CO CU +a — -4-3 33 C "8 - r. 03 'S CO to GO 9 o CO CO CO CO CO CO CO 5 b — ~ — ~ :- 3 3 o o E. O 5 C 3 O O _r: J= XI J XS X\ — -= CO o CO CN CO <N X DO i^ •* T 1 00 — CO -r 1 — i CO lO t^ o O O O o O o o o o ■4^ +3 ^M •+J •^ -*-> -^ ■+-» +3 Q CN tN 9 ■^ 1—i 00 ■o 00 CN IV 1^ CN tN -r t^ (33 1-1 O o <o CN O -f^ o co »\ • a> - i— » : CO C3 - - „ CO C "*< o (N XI O 3 o — 03 bC U zz a a OS £ 1 3 <— o to t^ V -^ tc 01 a 0) S3 BS !h CB C co >, -c a o a V m ■8*1 g Hi 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 AGRICULTURE. — The Publications of the Agricultural Experiment Station are sent gratis to citizens of the State of California. For detailed information regarding them address the Agricultural Experiment Station, Berkeley, California. 12 9802