486 THE STRUCTURE OF ECONOMIC PLANTS 



The Leaf. — The simple, entire leaves are spirally arranged 

 with a y^ phyllotaxy. There is a wide diversity of leaf form, and 

 they may be cordate, hastate, slightly to deeply lobed, or cut. 

 The apex and the lobes are acute or obtuse, the base is cordate to 



truncate; and, in some in- 

 stances, the midrib of the 

 leaf or leaflet is prolonged 

 beyond the blade to form 

 a short awn-like structure. 

 In general, the first leaves 

 are cordate, while those 

 formed later may be has- 

 tate, cut, or lobed. They 

 are equally variable with 

 respect to size, ranging 

 from 2.3^ to 6 inches in 

 their greatest dimension. 

 The venation is palmate, 

 the veins forming more or 

 less prominent projecting 

 ridges on both surfaces. 



The petiole varies from 

 2-3^ to 9 inches in length. 

 Its base may twine about 

 a support to some extent, 

 depending upon the variety, 

 and it is commonly thick- 

 ened, forming a cushion- 

 like structure on the lower 

 surface where it bends 

 sharply upward. The 

 . . , . n u adaxial surface is grooved 



Fig. 148. The origin of young sprouts from fleshy • 1 r i 



root. and, on either side of the 



petiole and just below the 

 blade, there are two small petiolar nectaries. Glandular hairs 

 occur on both surfaces but are more numerous on the abaxial one. 

 The Root. — The root system is adventitious (except in plants 

 grown from seed) and arises from fleshy roots, the stem, cuttings, 

 or young sprouts known as "draws" or sets. (Fig. 148.) Isbell 

 (5) has reported regeneration in leaf cuttings in which six different 



