NUTRITION AND SEASONAL LIFE OF PLANTS 135 



along the flower peduncles, into the ovaries and seeds which are 

 to form the apple crop for the current season. In addition to the 

 sugar and other soluble foods which enter the fruit and seeds 

 water must also be absorbed, particularly by the rapidly expand- 

 ing cells of the apples, since we know that the enlargement of cells 

 is almost entirely dependent upon water for the growing water 

 vacuoles. If the trees are prevented from overproduction of fruit 

 in any one season, they may repeat essentially the same reproduc- 

 tive history each season for a number of years, and this is one of 

 the methods now being used in the scientific fruit culture for 

 securing a uniform annual crop. If the trees overproduce in one 

 season, they must rest for a time in order to store up new reserves 

 in the trunk and branches for producing fruit in abundance. 



After the fruit is matured, the apple lays up a store of food 

 in the usual manner for its next season's spring growth of buds 

 and roots. The ripening of the fruit and seeds, and the shedding 

 of the leaves with the advent of frost, close this interesting and 

 active seasonal life of the apple tree, which may be taken as 

 typical of the life of our common trees and shrubs. 



SUMMARY 



We have now seen that the origin of annuals, biennials, and per- 

 ennials from the seed involves the same essential physiological proc- 

 esses. These processes include the active digestion and circulation 

 of reserve foods, respiration for the production of growth energy, 

 and, finally, adjusting movements for the proper placing of roots, 

 stems, leaves, and flowers in the soil, air, and sunlight. 



All of these plants have also an active summer period during 

 which food is manufactured, flowers are produced, and fruits and 

 seeds are matured. The differences between annuals, biennials, and 

 perennials consist largely, therefore, in the length of life of the 

 plant body and the consequent necessity of adapting this vegeta- 

 tive body to seasonal and climatic changes. In this adaptation of 

 the plant to the environment, annuals have a certain advantage in 

 maturing their seeds in one season, since the seed is a favorable 

 structure for distribution and for withstanding cold, drought, and 

 other environmental factors unfavorable to plant life. The annual 

 death of the plant body is therefore of no consequence as far as 



