CHAPTER XI 

 ECOLOGY OF LEAVES 



123. Ecology. — Plant ecology includes all that portion 

 of botany which has to do with the way in which plants 

 get on with their animal and plant neighbors, and espe- 

 cially the way in which they adjust themselves to the na- 

 ture of the soil and climate in which they live. Ecology, in 

 short, discusses the relations of plants to their surround- 

 ings or environment. A good deal of what has been said 

 in previous chapters about such topics as variation of roots 

 for life in air or water, parasitic plants, the occurrence of 

 winter bud-scales, is really ecological botany, although it 

 is not so designated in the sections where it occurs. 



124. Leaf Arrangement.' — As bas been learned from the 

 study of the leafy twigs examined, leaves are quite gener- 

 ally arranged so as to secure the best possible exposure to 

 the sun and air. This, in the vertical shoots of the elm, 

 the oak (Fig. 70), the apple, beech, and other alternate- 

 leaved trees, is not inconsistent with their spiral arrange- 

 ment of the leaves around the stem. In horizontal twigs 

 and branches of the elm, the beech (Fig. 71), the chestnut, 

 the linden, and many other trees and shrubs, the desired 

 effect is secured by the arrangement of all the leaves in 

 two flat rows, one on each side of the twig. The rows 

 are produced, as it is easy to see on examining such a 



1 See Kemer and Oliver's Natural History of Plants, Vol. I, pp. 396-424. 



105 



