OCCURRENCE 3 



reserve food-material as in the tubers of Cyperus esculenhis, 

 where it is associated with starch, and in the roots of some 

 orchids. 



This particular form of food reserve is doubly of value 

 since its presence may lessen the danger arising from drought, 

 and also more energy can be stored up in the form of oil than 

 in an equal bulk of carbohydrate ; in this connection may be 

 mentioned the fact that in some cases the appearance of oil 

 may be transient, thus in some trees the starch stored up in 

 the parenchyma of the stem may be converted into fat during 

 the winter's cold ; the starch, however, reappears on a rise in 

 temperature. Also fat or fat-like substances may appear in 

 the leaves of evergreen plants during the winter months. The 

 fat-like substances, according to Meyer,* who studied Vinca, 

 Taxus, and Ilex, do not show a seasonal variation in amount, 

 but continually increase with the age of the leaf. A low tem- 

 perature would appear to be a significant factor in this con- 

 nection. Thus Tuttle f found that plants of Linncsa borealis 

 exposed to a low temperature contained fat but no starch ; 

 on raising the temperature to 20° C, starch appeared in the 

 course of a day or two in a few plants, and in all cases after 

 the lapse of a week, during which period the plants were kept 

 in the dark. The controls, on the other hand, kept in the 

 dark at the low outside temperature gave no reaction for 

 starch. Plants containing much starch, on exposure to a 

 moderately low temperature, — 2° C, were found to lose 

 their starch and, concurrently, fat appeared. But if such 

 starch-containing plants were immediately exposed to very 

 low temperatures, — 15° to — 28° C, no reconversion ensued 

 and death took place. Lipase is present in the leaves of 

 plants showing these changes, and this, presumably, is part 

 of the mechanism of the change. Tuttle also found that all 

 evergreens growing in Northern Alberta contained little or no 

 starch but much fat by the end of October. All of the many 

 plants examined, Populus, Salix, Betula, Pyrola, Picea, etc., 

 with the exception of Lonicera glaucescens and Craiosgus, 



* Meyer : " Ber. deut. bot. Gesells.," 1918, 36, 5. 



t Tuttle : " Ann. Bot.," 1919. 33, 201 ; " Bot. Gaz.," 1921. 71, 146. 



