216 



ELEMENTARY STUDIES IN BOTANY 



bids protection during the winter. It is merely a balancing 

 between protection and work; the evergreens lay emphasis 

 on protection, and the deciduous plants on work. 



127. Special forms of leaves. We have been considering 

 leaves as foliage, but in many cases they are so modified that 

 they either lose their character as machines for the manufac- 

 ture of carbohydrate food, or add 

 to it some other work. In so far 

 as they remain green, they manu- 

 facture carbohydrates as do the 

 foliage leaves, but a definite change 

 in structure and behavior indicates 

 that they are constructed for some 

 other kind of work also. This 

 subject is a very extensive one, so 

 that only some of the conspicuous 

 illustrations will be noted. 



In certain situations leaves are 

 not free to develop to full size, 

 and when this happens they may 

 not develop chloroplasts, so that 

 they do not even become green. 

 Such leaves are called scales. They 

 are often called " reduced" leaves, 

 but they have not been reduced 

 from a larger size ; they have never 

 developed to a larger size. The 

 most conspicuous illustrations of 



scales are found among plants with subterranean stems 

 and in connection with " scaly" buds. One of the features 

 of a stem is to produce leaves, but underground stems 

 cannot produce foliage leaves unless, as in ferns, the leaves 

 reach the surface and develop in the light. When they 

 do not reach the surface, the leaves appear as small scale-like 

 bodies without green tissue. Often these scales seem to be 



FIG. 183. Pinnately compound 

 leaf of garden pea, whose ter- 

 minal portion has developed 

 as tendrils. After STRAS- 



BURGER. 



