134. GENERAL BOTANY 



period. This adaptation is secured by the woody character of the 

 stem, by the development of a protective cork jacket of bark, and, 

 except in pines and their relatives, by the seasonal shedding of 

 the delicate leafy portions of the plant with the advent of frost 

 or drought. In summer a woody plant is essentially a mesophyte, 

 that is, it is adapted to medium conditions of water and temper- 

 ature, while in winter, or during drought in dry regions, it par- 

 takes of the character of a xerophyte, that is, a desert plant. On 

 account of the great size and long life of woody plants, especially 

 trees, the seasonal life and the entire history of such a plant pre- 

 sents an interesting contrast to that of the other plants thus far 

 described. The following brief sketch of the life of an apple tree 

 will suffice to introduce the student to the characteristic life of 

 woody perennials. 



The first five or six years of the life of an apple tree are devoted 

 entirely to the building of a massive trunk with its great feeding 

 and absorbing root system and its extended branches for the sup- 

 port of an enormous leaf surface. The main trunk and branches, 

 as well as the large roots, here become the main storehouses into 

 which the excess of food is annually passed and stored in the 

 cortex, the rays, and the living cells of the wood and phloem. 



Each spring digestion takes place in these storage centers, 

 and food migration occurs along the usual channels to the grow- 

 ing parts of the tree. The wood rays supply food to the cambium 

 directly, the phloem carries food upward to the swelling buds 

 and downward to the growing root tips, while later movements 

 take place in all directions to growing cells in the phloem and 

 the wood. In this way the apple tree expands its leafy shoots 

 and forms new roots each spring for the season's work. When 

 the tree is well established, reproduction begins with the annual 

 production of flowers, which results in the formation of seeds and 

 fruit. After the reproductive phase begins in the life of a tree, 

 all excess food produced in the first months of each season by the 

 leaves, and a part of that previously stored in the trunk and 

 branches, goes largely into the forming of fruit. In the apple 

 tree, as in the sweet clover, the food streams are therefore diverted 

 from the storage tissues in the stem, the branches, and the roots, 



