Structure. 



65 



wide rounded sinuses and sharp, almost acuminate teeth. The apex is 



usually rounded, but somewhat emarginate in N. caerulea and sometimes 



in N. odorata, especially the variety gigantea. In the sinuate-margined 



Apocarpiae, the tendency is for the apex to lie in a sinus, while in 



Lotos the midrib is continued out into one of the serrations. At base 



the two lobes may overlap or just touch or divaricate in the same 



plant or species, so that this feature 



is of very little systematic value. 



Near the petiole the lobes may be 



fused by their edges for a distance 



of 2.5 to 5 cm. in Lotos, 1.3 cm. in 



some Apocarpiae, or almost none 



in Castalia ; this causes the leaf to 



be more or less peltate, and the 



fused portion I have called the pelta 



(Fig. 28, p). At the apex of the 



lobes they tend to develop distinct 



points marking off the borders of 



the sinus (the space between the 



lobes) from the rest of the margin 



of the leaf; this point is acuminate 



and sharp in N. gigantea, capensis, 



and the Lotos group, obtuse but still 



produced and evident in Castalia, 



altogether absent and the lobes 



broadly rounded in N. amazonum. 



The thickness of the leaves of 



most species gives them a leathery 



feeling, but they are rather brittle 



and easily torn. Mostly lying flat upon the water, we have exceptions 



in the crisped margins of JV. jlavo-virens, capensis, zanzibariensis and 



the Lotos group. N. odorata gigantea often has the margin of the 



distal half of the leaf turned up at right angles to the water-surface 



to the height of 2 or 3 cm., somewhat after the manner of Victoria. 



A rich chlorophyll-green is the usual color of the upper surface of 



the leaves. In N. flava, mexicana, tetragona, rubra-rosea, amazonum and 



zanzibariensis, however, there is more or less of brownish-red blotching, 



and in N. rubra the whole leaf is of a bronzy-red hue. The under 



surface of the leaf is quite different. Dull green in N. tuberosa, it is 



Fio. 28. Leaf of JV. flava, showing upper surface 

 on right, lower surface on left half ; a, angle of lobe ; 

 I, lobe; p, pelta; r, principal area; 8, sinus; t, 

 astomatic area ; 1, 2, 3, 4, 5, primary veins. 



