60 



A TEXTBOOK OF BOTANY [Ch. Ill, £ 



cold, and strong winds, — conditions which make transpira- 

 tion excessive. These conditions prevail in highest degree 

 in arctic, alpine, and desert regions, and there we find the 

 smallest leaves. In our native flora, the same principle is 

 exemplified in the plants of bogs, which are open cold places, 

 and in the evergreen trees, which have to withstand the rigors 



Fig. 30. — A view in Hawaii, showing the contrast between tall-growing 

 compound-leaved and low-growing simple-leaved Palms. (From Bailey, 



Cyclopedia of Horticulture.) 



of winter. Under conditions intermediate between the ex- 

 tremes, the leaves are intermediate in size, as our temperate 

 vegetation as a whole well illustrates. Correlatively, leaves 

 which grow exposed to similar general conditions approxi- 

 mate to a similar size, as well shown in our common deciduous 

 trees, where the leaves of Maples, Oaks, Chestnuts, Lindens, 

 Poplars, and others are not far from one size, or at least be- 

 ong to the same order of magnitude. 



Leaves which are morphologically large sometimes be- 

 come physiologically small by compounding of their blades to 

 separate leaflets (page 16 ; Figs. 32 and 37). The compound- 



