PHYSIOLOGICAL PROCESSES DURING FLOWERING 441 



cotton, etc. Very often, the fruit when shed has already reached 

 a considerable size and may be close to complete ripening. The; 

 main cause of shedding of the fruit is a deficiency of nutritive 

 substances, consumed rapidly when fruiting is simultaneous and 

 profuse. Many crop plants produce more flowers and set more 

 fruit than they are capable of maturing on account of the reserves 

 stored and the nutritive substances that the leaves continue to 

 elaborate; thus, very soon, an exhaustion of the reserves sets 

 in. It is very probable that there is a deficiency not only in 

 carbohydrates, proteins, fats, and such substances, but also in 

 specific hormones controlling the movement of these substances 

 toward the developing fruit. A struggle for the nutritive 

 substances takes place between the individual fruits. The first 

 that suffer are those that bore fewer or weaker seeds or are less 

 favorably situated in respect to food supply. After they have 

 ceased to obtain nutrients they drop off. Shedding represents 

 an active physiological process. In the flower peduncle, there 

 forms a special cork abscission layer, similar to that formed 

 when leaves are shed in autumn. This layer grows across the 

 tissues of the peduncle; when the abscission layer is complete, its 

 cells break apart, and the fruit falls of its own weight. 



As shedding usually occurs rather late, when a considerable 

 part of the nutritive substances is already transferred to the 

 fruit, it is accompanied by a useless expenditure of valuable 

 substances. In intensive horticultural practice, attempts are 

 made to avoid it by means of timely removal of flowers or very 

 young fruit. If it is desirable to obtain especially large fruit, 

 only a few of them are left to develop, all the others being 

 removed. This can be accomplished best before the fruit has 

 set. This method is widely applied in horticulture and garden- 

 ing, in the cordon culture of fruit trees, debudding, and stake 

 culture of tomatoes, etc. As the rapidly growing vegetative 

 shoots are also consumers of nutrients, it is advisable not to 

 allow an excessively vigorous growth of such shoots on fruiting 

 plants. The removal of suckers from corn and of water sprouts 

 from fruit trees is based on these considerations. 



In an arid climate, shedding of the fruit may be the result of 

 deficiency of water supply after the exhaustion of the soil mois- 

 ture or after excessive expenditure of water during desiccating 

 winds. Such a shedding is frequently observed, when cotton is 



