UNIVERSITY OF CALIFOBHIA PUBLICATIONS 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 BERKELEY, CALIFORNIA 
 
 A SPOTTING OF CITRUS FRUITS DUE 
 
 TO THE ACTION OF OIL LIBERATED 
 
 FROM THE RIND 
 
 BY 
 HOWARD S. FAWCETT 
 
 BULLETIN No. 266 
 
 Berkeley, Cal., February, 1916 
 
 UNIVERSITY OF CALIFORNIA PRESS 
 
 BERKELEY 
 
 1916 
 
Benjamin Ide Wheeler, President of the University. 
 EXPEEIMENT STATION STAFF 
 
 HEADS OP DIVISIONS 
 
 Thomas Forsyth Hunt, Director. 
 Edward J. Wickson, Horticulture (Emeritus). 
 
 Herbert J. Webber, Director Citrus Experiment Station; Plant Breeding 
 Hubert E. Van Norman, Vice-Director; Dairy Management. 
 William A. Setchell, Botany. 
 Myer E. Jaffa, Nutrition. 
 
 Eobert H. Loughridge, Soil Chemistry and Physics (Emeritus). 
 Charles W. Woodworth, Entomology. 
 Ralph E. Smith, Plant Pathology. 
 J. Eliot Coit, Citriculture. 
 John W. Gilmore, Agronomy. 
 Charles F. Shaw, Soil Technology. 
 
 John W. Gregg, Landscape Gardening and Floriculture. 
 Frederic T. Bioletti, Viticulture and Enology. 
 Warren T. Clarke, Agricultural Extension. 
 John S. Burd, Agricultural Chemistry. 
 Charles B. Lipman, Soil Chemistry and Bacteriology. 
 Clarence M. Haring, Veterinary Science and Bacteriology. 
 Ernest B. Babcock, Genetics. 
 Gordon H. True, Animal Husbandry. 
 James T. Barrett, Plant Pathology. 
 Fritz W. Woll, Animal Nutrition. 
 A. V. Stubenrauch, Pomology. 
 Walter Mulford, Forestry. 
 W. P. Kelley, Agricultural Chemistry. 
 Elwood Mead, Rural Institutions. 
 H. J. Quayle, Entomology. 
 J. B. Davidson, Agricultural Engineering. 
 H. S. Reed, Plant Physiology. 
 D. T. Mason, Forestry. 
 
 William G. Hummel, Agricultural Education. 
 Leon M. Davis, Dairy Industry. 
 John E. Dougherty, Poultry Husbandry. 
 S. S. Rogers, Olericulture. 
 *Frank Adams, Experimental Irrigation. 
 David N. Morgan, Assistant to the Director. 
 Mrs. D. L. Bunnell, Librarian. 
 
 * Tn co-operation Office of Public Roads and Rural Engineering, U. S. D. A. 
 
 CITRUS EXPERIMENT STATION 
 DIVISION OF PLANT PATHOLOGY 
 
 J. T. Barrett H. S. Fawcett 
 
 C. O. Smith 
 
A SPOTTING OF CITRUS FRUITS DUE TO THE ACTION 
 OF OIL LIBERATED FROM THE RIND* 
 
 By HOWARD S. FAWCETT 
 
 Among the various spots and blemishes of lemons and oranges 
 due to many different causes, there is one that is characterized by a 
 slight sinking of the tissue between the oil glands in the rind leaving 
 them standing out prominently over the surface of the affected areas. 
 These spots vary greatly in size and shape. They are usually circular 
 in outline and ordinarily do not exceed one-half an inch in diameter. 
 They may, however, be irregular in outline and at times involve the 
 greater portion of the surface of a fruit. At least one of the causes of 
 such spotting has been found by Mr. J. D. Culbertson and the writer to 
 be due to the remarkable and unexpected effect of small quantities 
 of oil liberated from the glands in the rind. The oil liberated from 
 the rind by any cause appears to act powerfully and quickly upon 
 all the cells at the surface with which it comes in contact, except 
 those immediately surrounding the oil glands. This leaves the oil 
 glands standing out prominently over the surface of the area occupied 
 by the spot. (Figs. 1 and 2.) 
 
 OCCURRENCE AND LOSSES 
 
 The greatest trouble from this spotting appears to occur in the 
 lemon packing houses, especially in moist cool weather, during the rainy 
 season. At that time, severe losses are often experienced by what is 
 known as the "green spot." The lemons which come to standard 
 size while green appear normal when picked, but on being set aside 
 to cure develop spots which remain green while the remainder of 
 the rind colors normally. (Fig. 2.) Such fruits may be kept for 
 weeks without enlargement of the spots and without change in their 
 green color. Sometimes the green is replaced after a long time by a 
 reddish or brownish color, but the normal color does not develop in the 
 spots. This lowers the grade of the fruit, but usually does not injure 
 seriously its keeping quality. Lemons that have already colored before 
 they are picked, may in some cases show spots of the same kind, though 
 not green and therefore less conspicuous. 
 
 * Paper No 23, Citrus Experiment Station, College of Agriculture, Univer- 
 sity of California, Riverside, California. 
 
 [261] 
 
262 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Fig. 1. — Immature oranges picked in November, showing the manner in which 
 the cells between the oil glands are broken down, leaving the oil glands stand- 
 ing out prominently over the surface of the green spots. 
 
 (Photographed by J. T. Barrett.) 
 
 
SPOTTING OF CITRUS FRUITS 263 
 
 Oranges picked too early or when they are immature may also 
 be severely affected by the "green spot." (Fig. 1.) Whether or not 
 the so-called "brown spot" that has caused much trouble in past 
 years during the winter months, is due in part to this cause has not 
 been determined. 
 
 EXPERIMENTS AND OBSERVATIONS LEADING TO THE CAUSE 
 
 The experiments of Mr. J. D. Culbertson of the Limoneira Com- 
 pany, Santa Paula, California, led to the discovery of at least one 
 cause of this green spotting. More than a year ago he produced what 
 appeared to be typical green spotting on lemons by pressing and roll- 
 ing them against boards. After putting them away for some weeks, 
 apparently tvpical green spots developed. At that time the spotting 
 was thought to be due to the injury to the cells themselves rather than 
 to the oil. It was also noticed at that time that fruit picked from 
 branches that had been cut off in pruning and were lying on the 
 ground developed more green spotting than others picked directly 
 from the trees. Other lemon growers had noticed that fruit picked 
 when dark green and wet usually developed more "green spot" than 
 similar fruit picked dry from the same trees. Mr. Culbertson states 
 that in washing a lot of lemons picked late in November, 1914, while 
 still wet with an early morning shower, a strong smell of lemon oil 
 was detected by the men at the washer as the fruit came through the 
 washing machine and that inspection of these lemons later showed 
 them to be severely injured from green spotting. This led them to 
 suspect that lemon oil itself might be responsible for the trouble, and 
 early in December, just after a shower, Mr. Culbertson injured some 
 lemons hanging on the tree so that the oil ran out over the uninjured 
 surface, and also placed some of this oil on the uninjured surface of 
 other fruits. The sinking of the tissue as in the green spot took place, 
 but the green color did not appear as it did on the stored fruit. It 
 was later found in our experiments that the green color rarely re- 
 mained on spots injured by lemon oil if the fruit were left on the tree, 
 but that if it were picked and stored the green color usually remained 
 fixed. 
 
 Dr. J. T. Barrett, in making observations in Tulare County in 
 December, 1913, noticed on the trees many fully colored oranges with 
 spots that probably had been typical green spots (or would have been 
 had they been picked earlier), that by remaining on the tree had 
 assumed almost the normal color of the fully colored rind. 
 
264 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 Fig. 2. — Cured lemons in November, showing the same type of spots as in 
 figure 1. The darker areas indicate the green spots that have developed in the 
 usual process of curing. 
 
 (Photographed by C. O. Smith.) 
 
SPOTTING OF CITRUS FRUITS 265 
 
 FURTHER EXPERIMENTS WITH LEMON AND ORANGE OIL 
 
 In an experiment by the writer, begun in February, 1915, the 
 typical green spots were developed by very small amounts of lemon 
 oil acting on the uninjured surface of green lemons in moist jars. 
 Twelve lemons were picked very carefully to avoid any injuries on 
 February 17, 1915, while they were still wet from a rain. Three lots 
 of four each were placed in moist jars. On the uninjured upper 
 surface of the first lot, a small amount of oil from a portion of the 
 peel of another green fruit was squeezed out by hand. A small area 
 on the rind of each of the second lot was pressed with the blunt end 
 of the flat handle of a scalpel until oil was seen to appear on the 
 surface. The third lot was left untreated as checks. The jars were 
 kept covered to retain the moisture. On March 18, 1915, all the fruits 
 in the first lot on which the lemon oil had remained on the uninjured 
 surface showed typical spots where the oil had broken down the tissue 
 between the oil glands. On two, the spots were green and on the 
 others, they were reddish to brownish. The portion of the surface 
 unspotted was coloring in the normal way. The second lot of fruits 
 which had been pressed with the end of a scalpel, showed the same 
 kind of spots. The spots were larger that the actual area pressed by 
 the scalpel handle due to the spreading of the oil over the uninjured 
 surface beyond the bruised spot. On the third lot kept as checks no 
 spotting occurred. 
 
 Another experiment with lemons to compare the effect of lemon 
 oil on dry and moist fruits was begun March 4, 1915. Four jars 
 with four fruits each were prepared. For the first, the green fruits 
 freshly picked from the trees were put in dry without washing and 
 the lemon oil squeezed on a portion of their uninjured surfaces and 
 the jar left open. For the second, the fruit was first washed and 
 placed in the jar wet and the lemon oil squeezed on as in the first 
 and the jar covered. The third and fourth jars were for checks, the 
 fruit for one being put in dry and the jar left open, and the fruit 
 for the other being washed and the jar covered. Three out of four 
 of the first lot kept dry showed spots on March 18th, only one of 
 which was green. All in the second lot kept wet, showed typical spots 
 while none of the fruits on which no lemon oil was squeezed in the 
 two check jars showed any spots. 
 
 Besides experiments with oil squeezed directly from the living 
 rind of other fruit, experiments were also tried with measured quan- 
 
266 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 tities of commercially expressed lemon oil.* This lemon oil acted on 
 the rind in the same manner as the oil squeezed directly from the 
 living rind. 
 
 In conducting experiments with lemon oil, it was observed that 
 the action of the oil in breaking down the tissue was very rapid. In 
 order to find out something as to the length of time necessary for 
 the oil to produce visible injury, the following experiment was tried : 
 
 Nineteen full-sized light green lemons were placed in a row on 
 the table in the laboratory and drops containing one one-hundreth 
 (0.01) of a cubic centimeter were dropped on each. The drop on the 
 first was rubbed off immediately with a piece of cotton. The other 
 drops were rubbed off after they had remained on the rind different 
 periods ; namely, 3, 6, 7, 8, 9, 10, 15, 20, 30, and 45 seconds ; 1, 2, 5, 
 10, 20, and 30 minutes ; 1 and 2 hours, respectively. A visible effect 
 of the oil was seen in a very short time on those left on two or more 
 minutes. On the one on which the oil had acted 2 minutes a slight 
 effect was visible in 20 minutes after the oil was rubbed off, and on 
 the one on which the oil had acted 5 minutes, the effect was visible 
 in 10 minutes after the oil was rubbed off. In 24 hours the fruit on 
 which the oil had acted for approximately 8 seconds, showed a slight 
 effect. On all those on which the oil had acted less than 8 seconds, 
 no effect was visible, even after several weeks. The severity of effect 
 was in proportion to the length of time the oil had acted upon the rind 
 with slight variations, probably due to differences in the fruit. The 
 experiment showed clearly that the action of the oil in breaking down 
 the surface cells is extremely rapid. 
 
 During the months of March and April, a large number of different 
 experiments were carried out by putting different quantities of lemon 
 and orange oil from the rind on more than 150 fruits of all ages of 
 both lemons and oranges. The effect of the oil was further compared 
 in both moist and dry atmosphere on fruit both on and off the tree. 
 The effect of the oil was also tested on young shoots, leaves and flower 
 buds. The following is a summary of the results of the various ex- 
 periments : 
 
 1. The effect of a given amount of oil from the rind was greater 
 on fruit in a moist atmosphere than on similar fruit in a dry atmos- 
 phere. 
 
 2. The moisture being the same, the effect was greater on green 
 or immature fruit than on fully colored or mature fruit. 
 
 * I am indebted to Mr. C. P. Wilson, of the Citrus By-Products Laboratory 
 of the Bureau of Chemistry, United States Department of Agriculture, Los 
 Angeles, California, for two samples of lemon oil for use in the experiments. 
 
spotting of errors fruits 267 
 
 3. The effect was greater on fruit just picked than on similar 
 fruit picked for some days. 
 
 4. The action of small amounts of oil, for example, such as could 
 be liberated by a hard pressure of the thumb against the rind of a 
 dark green freshly picked moist lemon (or by .01 cc. of the com- 
 mercially expressed lemon oil), was sufficient to cause the typical green 
 spotting. The green color appeared to be fixed in the portion acted 
 on by the oil while the remainder of the rind colored normally in the 
 usual process of curing in four to six weeks. 
 
 5. The action of a large amount of lemon oil, such as one-tenth 
 of a cubic centimeter or more, under the same conditions caused the 
 spots to' become brownish or reddish rather than green. When the 
 amount was sufficiently increased the breaking down of the tissue was 
 so great that blue mold started in a few days. 
 
 6. When the fruits acted on by the oil were left attached to the 
 tree, only in rare cases did the green color remain. As the fruits 
 continued to grow and mature, the sunken areas were partially restored 
 and only slight scars were left. 
 
 7. Under similar conditions the oil from the rind of oranges acted 
 upon other uninjured oranges in the same manner as did the oil from 
 the rind of lemons act upon other lemons. 
 
 8. The oil caused the spotting of tender leaves and shoots and 
 the withering of flower buds when squeezed out upon them. 
 
 9. The action of the oil on the surface of the rind is extremely 
 rapid, as shown by the fact that one one-hundreth of a cubic centi- 
 meter of lemon oil acting for eight seconds was sufficient to show 
 afterward a visible effect on the rind. 
 
 The results of these experiments aid us in explaining some of the 
 following observed facts in connection with the occurrence of the so- 
 called green spot. 
 
 Green spotting has been observed almost exclusively on fruit picked 
 during the late fall, winter and early spring. This in general corres- 
 ponds to the season of moist atmospheric conditions in California due to 
 frequent rains and fogs. It has also been observed, as stated before, 
 that fruit picked while wet after a rain is more apt to spot than that 
 picked dry. The experiments have shown that the same quantities of 
 oil, other things being equal, has more effect in a moist than in a 
 dry atmosphere, on wet than on dry fruit. The lemons picked at 
 the above mentioned season are apt to contain a higher percentage of 
 dark green fruit that at other seasons. The experiments have also 
 shown that the oil had more effect on green than on ripe fruit. The 
 explanation would therefore appear to be this; that in the process of 
 
268 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 picking and handling, certain small amounts of oil are liberated on 
 the surface of the rind, and that this oil is able to cause severe spotting 
 in a moist atmosphere or when the fruit is wet, as is often the case 
 during the rainy season, especially when it is green. That no serious 
 trouble from green spotting is experienced in summer is probably 
 due to the dryer atmosphere and the greater maturity of the fruit. 
 In a dry atmosphere the oil would quickly volatilize and therefore 
 have little time to act. 
 
 Then there occur spots on fruit on the tree in connection with 
 scratches or bruises from passing teams that in size appear to be out 
 of all proportion to the mechanical injury inflicted. In many cases 
 an area may be traced where the oil has spread out from the broken 
 cells affecting the adjacent tissue in the same manner as in the spotting 
 under consideration. It also seems probable that in like manner the 
 injury following red spider, and other mites and insects is emphasized 
 by the liberation of oil. The injuries due to the whipping of the fruit 
 against the branches by the wind in severe storms are also probably 
 more severe for the same reason. 
 
 It has also been observed by packing-house men that there is great 
 variation in the spotting between fruit from various groves handled 
 under the same conditions. This may be due in part to variations in 
 maturity or growth conditions of the fruit that might modify the 
 structure of the rind and possibly the amount of oil in it. The oil is 
 probably liberated much more easily from fruits from certain groves 
 than others, due possibly to these differences in the fruit itself. 
 
 EEMEDIES 
 
 One very obvious remedy is to avoid picking fruit when wet either 
 with rain or dew. That this has proved to be a practical remedy in 
 some cases is shown by the following examples. 
 
 Mr. Culbertson of the Limoneira Company, Santa Paula, writes : 
 "Since the first of December we have carefully avoided picking lemons 
 too soon after a rain or extra heavy dew, until it developed that we 
 were getting practically no green spot. The disappearance of the spot 
 later was probably due also to the greater maturity of the lemons." 
 
 Mr. M. Perry of the Teague McKevitt Ranch, showed the writer 
 two sets of lemons, one set picked in the early morning after a rain, 
 the other picked from the same trees and by the same pickers near the 
 middle of the same day when the fruit was dry. The first lot picked 
 
SPOTTING OF CITRUS FRUITS 269 
 
 wet was badly spotted; the second, picked dry, showed only an 
 occasional spot. 
 
 Another remedy that suggests itself, is extreme care in handling 
 the fruit to avoid injuries or knocks that would tend to liberate the 
 oil in the rind. It has been recognized for a long time that great care 
 in handling the fruit is necessary in avoiding decay from blue mold. 
 To avoid green spotting on susceptible fruit during the critical season 
 even greater care will doubtless be necessary. Pressing together of the 
 fruit in the picking sacks, letting them drop too far into the field 
 boxes, jolting in wagons without springs on rough roads, rough knocks 
 and jamming in washing, grading and packing are all means that 
 would tend to liberate the oil from the rind. 
 
STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION 
 
 REPORTS 
 
 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viticultural 
 Report for 1896. 
 
 1902. Report of the Agricultural Experiment Station for 1898-1901. 
 
 1903. Report of the Agricultural Experiment Station for 1901-03. 
 
 1904 Twenty-second Report of the Agricultural Experiment Station for 1903-04. 
 
 1914. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1913-June, 1914. . 
 
 1915. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1914-June, 1915. 
 
 No. 
 168. 
 
 169. 
 174. 
 
 178. 
 184. 
 
 185. 
 
 195. 
 197. 
 
 198. 
 203. 
 
 207. 
 208. 
 212. 
 213. 
 216. 
 
 220. 
 225. 
 
 227. 
 230. 
 
 BULLETINS 
 No. 
 
 Observations on Some Vine Diseases 
 in Sonoma County. 
 
 Tolerance of the Sugar Beet for Alkali. 
 
 A New Wine-Cooling Machine. 
 
 Mosquito Control. 
 
 Report of the Plant Pathologist to 
 July 1, 1906. 
 
 Report of Progress in Cereal Investi- 
 gations. 
 
 The California Grape Root-worm. 
 
 Grape Culture in California ; Improved 
 Methods of Wine-making ; Yeast from 
 California Grapes. 
 
 The Grape Leaf-Hopper. 
 
 Report of the Plant Pathologist to 
 Julv 1, 1909. 
 
 The Control of the Argentine Ant. 
 
 The Late Blight of Celery. 
 
 California White Wheats. 
 
 The Principles of Wine-making. 
 
 A Progress Report Upon Soil and Cli- 
 matic Factors Influencing the Com- 
 position of Wheat. 
 
 Dosage Tables. 
 
 Tolerance of Eucalyptus for Alkali. 
 
 Grape Vinegar. 
 
 Enological Investigations. 
 
 234. 
 241. 
 242. 
 244. 
 246. 
 248. 
 
 249. 
 250. 
 251. 
 
 zoz. 
 
 253. 
 
 254. 
 255. 
 256. 
 
 257. 
 258. 
 261. 
 
 262. 
 
 263. 
 
 264. 
 
 Red Spiders and Mites of Citrus Trees. 
 Vine Pruning in California, Part I. 
 Humus in California Soils. 
 Utilization of Waste Oranges. 
 Vine Pruning in California, Part II. 
 The Economic Value of Pacific Coast 
 
 Kelps. 
 Stock-Poisoning Plants of California. 
 The Loquat. 
 Utilization of the Nitrogen and Organic 
 
 Matter in Septic and Imhoff Tank 
 
 Sludges. 
 Deterioration of Lumber. 
 Irrigation and Soil Conditions in the 
 
 Sierra Nevada Foothills, California. 
 The Avocado in California. 
 The Citricola Scale. 
 Value of Barley for Cows Fed Alfalfa. 
 New Dosage Tables. 
 Mealv Bugs of Citrus Trees. 
 Melaxuma of the Walnut, "Juglans 
 
 regia." 
 Citrus Diseases of Florida and Cuba 
 
 Compared with Those of California. 
 Size Grade for Ripe Olives. 
 The Calibration of the Leakage Meter. 
 
 No. . ., , 
 
 65. The California Insecticide Law. 
 
 69. The Extermination of Morning-Glory. 
 
 70. Observations on the Status of Corn 
 
 Growing in California. 
 76. Hot Room Callusing. 
 80. Boys' and Girls' Clubs. 
 
 82. The Common Ground Squirrels of 
 
 California. 
 
 83. Potato Growing Clubs. 
 
 100. Pruning Frosted Citrus Trees. 
 
 106. Directions for Using Anti-Hog Cholera 
 
 Serum. . 
 
 107. Spraying Walnut Trees for Blight and 
 
 Aphis Control. 
 
 108. Grape Juice. . 
 
 109 Communitv or Local Extension Work 
 by the High School Agricultural De- 
 partment. 
 
 110. Green Manuring in California. 
 
 111. The Use of Lime and Gypsum on Cali- 
 
 fornia Soils. . 
 
 113. Correspondence Courses in Agriculture. 
 
 114. Increasing the Dutv of Water. 
 
 115. Grafting Vinifera Vineyards. 
 
 117. The Selection and Cost of a Small 
 
 Pumping Plant. 
 
 118. The County Farm Bureau. 
 
 119. Winery Directions. . 
 
 121. Some Things the Prospective Settler 
 
 Should Know. 
 
 122. The Management of Strawberry Soils 
 
 in Pajaro Valley. 
 
 CIRCULARS 
 No. 
 
 124. 
 125. 
 126. 
 127. 
 128. 
 129. 
 130. 
 131. 
 132. 
 
 133. 
 134. 
 135. 
 136. 
 137. 
 138. 
 139. 
 
 140. 
 
 141. 
 
 142. 
 
 143. 
 
 144. 
 145. 
 
 146. 
 
 Alfalfa Silage for Fattening Steers. 
 
 Aphids on Grain and Cantaloupes. 
 
 Spraying for the Grape Leaf Hopper. 
 
 House Fumigation. 
 
 Insecticide Formulas. 
 
 The Control of Citrus Insects. 
 
 Cabbage Growing in California. 
 
 Spraving for Control of Walnut Aphis. 
 
 When to Vaccinate against Hog 
 Cholera. 
 
 County Farm Adviser. 
 
 Control of Raisin Insects. 
 
 Official Tests of Dairy Cows. 
 
 Melilotus Indica. 
 
 Wood Decay in Orchard Trees. 
 
 The Silo in California Agriculture. 
 
 The Generation of Hydrocyanic Acid 
 Gas in Fumigation by Portable Ma- 
 chines. 
 
 The Practical Application of Improved 
 Methods of Fermentation in Califor- 
 nia Wineries during 1913 and 1914. 
 
 Standard Insecticides and Fungicides 
 versus Secret Preparations. 
 
 Practical and Inexpensive Poultry Ap- 
 pliances. . 
 
 Control of Grasshoppers in Imperial 
 Valley. 
 
 Oidium or Powdery Mildew of the Vine. 
 
 Suggestions to Poultrymen concerning 
 Chicken Pox. 
 
 Jellies and Marmalades from Citrus 
 Fruits.