8 



A TEXT-BOOK OF BOTANY 



incline to broader forms than leaves pinnately veined or 

 parallel-veined. Names have been given to the various leaf 

 forms, as linear, lanceolate, ovate, orbicular, etc., but they 

 can be learned as they are needed. In the net-veined 

 leaves the margin of the blade may be more or less deeply 

 toothed or lobed (Fig. 2, B) ; but in the parallel- veined leaves 



the margin is not at all 

 toothed, in which case 

 the leaf is said to be en- 

 tire (Fig. 2, C). It is 

 quite common also for 

 net-veined leaves to 

 branch, when they are 

 said to be compound. 

 In this case the leaf- 

 blade is broken up 

 into a number of small 

 blades, sometimes very 

 many of them, called 

 leaflets. A branching 

 pinnate leaf is said to 

 be pinnately compound 



FIG. 3. Compound leaves : A, pinnately com- (Fig. 3, A)', and a 

 pound leaf of black locust ; B, palmately com- branching palmate leaf, 

 pound leaf of red clover, with three leaflets, 



also showing stipules. palmately compound 



(Fig. 3, B). 



12. Exposure to light. The special work of leaves is ex- 

 ceedingly important, and this work cannot be done unless 

 the leaf is exposed to light. This fact explains many 

 things in connection with the position and arrangement 

 of leaves. Leaves must be arranged to receive as much light 

 as possible to help in their work, but too intense light is 

 dangerous; hence the adjustment to light is a delicate one. 

 The exact position any particular leaf holds in relation to 

 light, therefore, depends upon many circumstances, and 



