238 



LEAVES 



light, therefore, is a delicate one, and many leaves do not have 

 the proper amount of light. 



The more or less horizontal position which the leaves of many- 

 plants assume enables them to receive the direct and most in- 

 tense rays on their upper surface. Leaves in this position receive 

 more light rays than those having the oblique or vertical position. 



Fig. 220. — Leaves divided into leaflets. A, 

 leaflets. B, Walnut leaf having many leaflets, 

 stipules; b, bud. 



leaf of Alfalfa with three 

 I, leaflets; p, petiole; s, 



The separation of leaves through the elongation of the internodes 

 is another means of securing better exposure. For example, dur- 

 ing the early growth of the Corn plant, the leaves are closely 

 packed around the growing point of the stem and only the outer 

 ends of the blades are well exposed. But through the elongation 

 of the internodes, all of the leaves are finally separated, so that at 

 the time the tassel and ears appear all portions of the leaves 

 receive light. 



The way leaves are arranged on the stem is a' so an important 

 feature in securing proper exposure. There are three coimnon 

 arrangements, alternate, opposite, and whorled. In the alternate 

 arrangement, there is but one leaf at a node and they appear to 

 alternate, first on one side of the stem, then on a different side. 



