234 THE PHYSIOLOGY OF PLANTS 



which ill general parlance are termed fruits. Now we shall 

 discuss the processes by means of which the character of the 

 fruits may be changed and improved. 



In the case of the fruits used for dessert, it is essential to 

 increase their number, size, appearance, and flavour. 



An increase in the number of fruits demands an increase in 

 the number of flower-buds, and as these are generally formed 

 in the preceding season, the horticulturist must extend his 

 operations to that period. Everyday experience teaches us 

 that the period of sexual reproduction does not, as a rule, set 

 in until the vegetative growth (production of leaves) begins to 

 diminish or to cease entirely. The function of the leafy tissue 

 is to form new organic food material from the raw material 

 contained in the soil as inorganic salts and in the air as carbonic 

 acid. The stronger the young embryo, the stronger will be the 

 growing seedling — that is, the active plant. The larger and 

 more numerous the organs and the greater the quantities of 

 raw material which they can assimilate in a given time, the 

 greater will be the number of new assimilating organs which 

 the plant will develop. The longer these organs function, the 

 greater will be the amount of substances assimilated. 



The duration of the assimilating period, and the way in 

 which the products are used up, depend partly upon the 

 season in which the vegetative period falls. In the case of 

 plants left to themselves, the germination of the seeds and 

 the development of leaves in trees and shrubs takes place 

 in spring, when the soil is moister, but during which period 

 there is less light and heat than in summer. This combination 

 of circumstances proves to be very beneficial for the develop- 

 ment of leaves. On the other hand, the foliage is smaller, the 

 shoots shorter, and the number of lateral branches smaller, and 

 their development less extensive, if the vegetative period is 

 artificially postponed until the summer, or if the spring is 

 abnormally dry and warm. The plant will under such cir- 

 cumstances very soon come to an end of its vegetative period, 

 and begins at once to use the assimilated substances for the 

 period of sexual development. 



If, however, the first period is lengthened by artificial shading, 

 copious watering, and rich nutrition, or if a moist spring is 



