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 has 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 Kerner and Oliver’s Natural History of Plants, Vol. I, pp. 396-424. 
105 
