104 BEITISH 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 stiQ 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, markuig 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 



