80 



THE LEAF 



the dissected or the slender conformation; in so far as the 

 water supports the weight, to that extent a compact and 

 rigid framework is rendered unnecessary. He compares 

 such leaves as those of Cabomba (Fig. 64) to the gills of 

 fishes, which while in water float apart, but have not enough 

 strength to support their own weight, and consequently 

 collapse in air. 



133. Finally^ it is evident that in running water and 

 in waves the slender forms give readily to the movements 

 of the water, and are therefore less likely to be torn than 

 broader forms would be. 



134. Floating leaves show as pronounced a tendency to 

 become circular as the submeroced ones to become linear. 

 The circle, or ellipse, may be complete with the leaf stalk 



65. Floating leaves : a, of the Water Shield ; h, of the Water Lily. 



running to the center, as in the Water Shield (Fig. Qb^a). 

 In this case, the form is said to be 2:)eltate. Or tlie circum- 

 ference may be interrupted by a cleft, or sinus^ leading to 

 the summit of the petiole Qe.g. the Water Lily, Fig. 6b^ b'). 

 The point of attachment of blade and petiole is the real 

 base of the blade. The circle is filled out, in fact, by the 

 growing backward of the blade at eacli side of the base. 

 This leaf is described as orbicular, and cordate (heart- 

 shaped), or cordate cleft, at the base. 



135. We may suppose that the circle is the most advan- 

 tageous form in leaf building, since the parts are equi- 

 distant from the petiole, and thus conduction of food 



