THE INITIATION OF THE REPRODUCTIVE PROCESSES 183 



ence is associated with circumstances making for carbohydrate accumula- 

 tion in fruitful plants rather than a difference in the method of carbo- 

 hydrate utilization. In other words, the carbohydrate supplied must be 

 in excess of the amount used. 



Carbohydrate accumulation depends primarily on light conditions. Under 

 experimental conditions carbohydrate assimilation varies with light intensity, 

 in the absence of other limiting factors; however, other factors become limiting 

 for plants grown in the open, so that carbohydrate assimilation and hence car- 

 bohydrate accumulation depends on the number of hours of sunlight rather than 

 on the hght intensity. ^^'^ Garner and Allard^i have shown experimentally that 

 an increase in the duration of light exposure determines f ruitfulness in some plants 

 and they suggest that the daily increase in duration of illumination which reaches 

 a maximum on June 21, may have an important relation to the time at which 

 these plants blossom. It is interesting to observe that fruit bud differentiation 

 in the apple usually occurs the latter part of June or early part of July, though 

 it has been observed to occur at almost every season. However, Garner and 

 Allard found that many plants do not blossom unless the duration of light exposure 

 is short. Voechtingi^- found that a decrease m light intensity reduced the number 

 of blossoms and eventually prevented flowering altogether in some plants, while 

 in others there was a tendency for the development of cleistogamous flowers. 



Klebs"" found that when blossoming depends on the intensity of illumination, 

 red hght which is the most effective in photosynthesis is essential, blue light 

 having much the same effect as darkness. 



Defoliation previous to the period of fruit bud differentiation obviously 

 interferes with carbohydrate manufacture and the recent work of Harvey^" shows 

 that this is reflected in the chemical composition of defoliated apple spurs which 

 contain less hydrolyzable polysaccharides and total carbohydrates than normal 

 spurs. This is particularly important in connection with the decreased fruit 

 bud differentiation observed by Harvey on defohated fruit spurs. 



In Fruit Spurs. — Hooker^"^ in a study of the seasonal changes in the 

 chemical composition of apple spurs of certain varieties and bearing 

 habits found that, when there was a relatively low total nitrogen content, 

 starch accumulation occurred while fruit buds were being differentiated. 

 When there was a relatively high total nitrogen content, starch accumula- 

 tion did not occur at the same time, though it followed later, and the 

 spurs remained vegetative for another year. These conditions, were 

 found in spurs showing characteristically different behavior regardless 

 of whether spurs of only one or of several different bearing habits were 

 found on the same tree at one time. Some of these results, shown 

 graphically in Figs. 22 and 23, emphasize two principles involved in the 

 development of the fruitful condition; (1) At certain critical periods in the 

 life of the plant, its activities are directed into one channel or another, 

 depending on the nature of the conditions affecting its equilibrium at that 

 particular time. This lends weight to Kraus and Kraybill's surmise 



