334 TEXTBOOK OF BOTANY 



of flower formation. Their first appearance can be detected only by 

 examining thin sections of buds with a microscope. During the winter 

 many of the buds of trees and shrubs contain rudimentary flowers that 

 may be recognized without a microscope (Chapter XXVI). Evidently 

 the initiation of these dormant rudimentary flowers occurred sometime 

 during the previous growing season. 



In the latitude of Ohio the initiation of flower buds on trees of apple, 

 peach, plum, and cherry usually occurs sometime during the last two 

 months of summer. The initiation of flower primordia in many shrubs, 

 such as currants, gooseberries, and cranberries, also occurs during these 

 months. In the early spring-flowering plants that grow from the terminal 

 bud in bulbs, the differentiation of flower primordia occurred sometime 

 during the preceding growing season. 



The opening of flower buds, the relatively rapid enlargement of the 

 different parts of flowers, and the subsequent development of fruits the 

 following spring are familiar to all. In annuals, biennials, and many 

 herbaceous perennials, the initiation of flower primordia and the subse- 

 quent development of flowers and fruits occur during the same season. 



Since the fruit and the parts of a flower are composed of cells, one 

 may reasonably infer that the processes of growth in them are similar to 

 those in leaves, stems, and roots. Here again the formation, enlargement, 

 and differentiation of cells are influenced by food, water, hormones, and 

 all the other factors that affect the growth of cells. As in leaves, an absciss 

 layer may develop at the base of each of these floral structures, and they 

 may abscise and fall off at maturity or in some earlier stage of develop- 

 ment. During certain years this abscission may be so excessive that the 

 ground beneath a tree is covered with a laver of abscised flowers and 

 young fruits. Biloxi soybeans which grow where they are exposed to 

 light 14 to 15 hours each day may bloom, but no fruits develop. The 

 initiation of flower primordia, therefore, may occur when conditions are 

 unfavorable to the further development of both flowers and fruits. It is 

 because of this fact that attention has been called to each of these three 

 processes: initiation of flower primordia, flowering, and fruiting. In the 

 cultivation of plants one strives to maintain a combination of conditions 

 that is favorable to all three of these processes. 



The formation of seeds in fruits is dependent upon the formation of 

 pollen and gametes and is the result of a long series of processes that 

 will be considered in Chapter XXXIII. These, too, are influenced by ex- 

 ternal conditions. 



