CH. Ill, 8] FORMS OF FOLIAGE LEAVES 63 



leaves which float on the water, as with Water-lilies ; while 

 climbing Ivies show the same tendency, usually modified, 

 however, by marked angularity of form. The full exposure 

 of the round blades to light is aided by adjustments in the 

 slender petioles, and it is in such plants that leaf-mosaics, 

 mentioned in the preceding section, become the most perfect. 

 Linear leaves are typified by those of the Grasses, with their 



FIG. 33. Leaves approximating to orbicular shape; X |. Garden Nas- 

 turtium, Yellow Water-lily, Pelargonium, English Ivy, Ground Ivy. 



slender elongated blades merging imperceptibly into the pet- 

 ioles, and their approximately equal-sized parallel veins 

 joined by inconspicuous veinlets (Fig. 34). Such leaves 

 occur chiefly in dense growths in the most brightly lighted 

 places, either upright and parallel like the Grasses in meadows 

 or the Cat-tails along lake sides, in dense radiating heads like 

 the Bunch-grasses and Spanish Bayonets (Fig. 35), or else in 

 mats and tufts, as along the branches of our evergreen trees. 

 At first thought it would seem that such leaves, presenting 

 their edges rather than their faces to the sun, must be badly 

 illuminated. Yet their habitual occurrence in the sunniest 



