[Chap. IX ENVIRONMENT AND LEAF DEVELOPMENT 



83 



Fig. 42. The English gorse growing in moist places has leafy shoots; in dry situa- 

 tions the shoots are largely spines and thorns. After Lothelier. 



Some of the variations observable in leaves that grow out-of-doors are 

 the results of changes in such factors as light and water, similar to those 

 discussed in this chapter. When individuals of the same species grow in 

 very dissimilar habitats, environmental effects on leaf forai often make 

 it difficult to identify the plants. Kevs to plant species are based on 

 heritable characteristics as developed in a single natural habitat, prefer- 

 ably a favorable one. 



