104 BRITISH PLANTS 
leaf is a xerophytic form adapted to live through the 
winter, and that the purpose of its special characters is 
to reduce loss of water by transpiration within safe 
limits. The leaf of the lime has no such characters ; it 
is equipped for summer use only. Again, assimilation 
is not so active in the holly as in the lime. A lack of 
nutrition is the result, and this is actually expressed in 
the leaf by the spines. The spines are modified vein- 
structures between which the leaf-tissue has failed to 
develop. On well-grown plants growing in good soil the 
leaves tend to lose their spines because they are better 
nourished. 
Thus each leaf has written upon it functional signs 
that the physiologist can read, even if only imperfectly. 
We understand a structure when we know the reason for 
it—that is, when we know its function. A plant is a 
living thing. It lives in a certain environment, and the 
nature of that environment, acting through its vital 
functions, is expressed in its outward form and inward 
structure. 
The study of organisms as living things is Biology 
(Gr. bios, life). To connect form with function, and both 
with environment, is to make botany a biological study. 
With morphology alone we have little to do ; in ecology, 
morphology is quite dominated by biology. 
This biological method of looking at plants is quite 
recent. It requires an accurate knowledge of the main 
facts of physiology, and this our forefathers did not have. 
Physiology grew as the science of chemistry and physics 
developed. But our ancestors saw form clearly enough, 
although they knew little of the functions that underlie 
form, and still less of the relations between form and 
environment. The early botanists studied plants as they 
found them—in the garden, in the field, in the herbarium. 
They examined the outward form, marking and recording 
resemblances and differences. Upon these morpho- 
logical characters they founded their classifications and 
generalizations. It must be granted, however, that 
broad or general views can only be obtained when plants 
are collected into groups, and the simplest and most 
natural groupings are those which are founded upon the 
resemblances and differences of external form. 
Even at the present time it is found convenient for 
