MORPHOLOGY, GENETICS AND BREEDING 47 



green, dark blue green, pea green or yellow green. In A. hypogaea this 

 variation is pronounced and has been shown to be genetic in origin. The 

 dark dull green of one tuberous-rooted wild species {A. marginata) has 

 not been seen in A. hypogaea but is approached in certain Chinese forms. 

 The genetic segregation for depth of chlorophyll green in A. hypogaea 

 leads to the general supposition that the variations in leaf color between 

 wild species are also genetic in nature and are not primarily a matter of 

 mineral nutrition as might be suggested by cultivated fields of A. hypo- 

 gaea differing in available nitrogen, calcium, and other mineral elements. 



The arrangement of the leaves on A. hypogaea is intimately associ- 

 ated with the branching habit of the plant. The leaves occur alternately, 

 one at each node, and describe a 2/5 phyllotaxy (Richter, 59). Embry- 

 onic leaves on the main stem axis are well formed and ordinarily saow 

 little or no reduction in size. This is far from the case on all primary 

 and secondary laterals. As one proceeds towards the base from the tips 

 of such branches, the leaves usually show reduction in size and at the 

 lowermost nodes also show a reduction in number of parts and complete- 

 ness of form until at the first and usually the second node, the leaves are 

 represented by mere scales known as cataphylls. Branches arising in the 

 axils of the foliage leaves may be either vegetative or reproductive. In 

 either case the first two nodes are cataphyllar. 



The morphology of the mature foliage leaf of cultivated peanuts has 

 been described rather completely. The leaf is even-pinnate with four 

 obovate to elliptical leaflets. Two large, long-lanceolate stipules enclose 

 the leaf in the bud. Stomata occur on both surfaces of the leaves. Varia- 

 tions in organization of leaves of seedlings and older plants include oc- 

 casional quinque-foliate, trifoliolate, bifoliolate, and even unifoliolate 

 types. 



Reed (55) illustrated sections of the leaflets and emphasized the 



presen££_i2f_water_stoo^£.j;dkJILjhS-.£E2^ This water 



storage tissue, associated with typical mesophytic leaf structure, led him 

 to speculate concerning the intermediate ecological position of the peanut 

 betwee n xerophyte and mesophyte. These speculations may prove to be 

 well founded, for peanuts are capable of withstanding long periods of 

 dry weather but give a typical mesophytic response to relief by rains. 

 The peanut's ability to withstand adverse water conditions, its adaptation 

 to soils of deep sand, and its geocarpic habit conform to what we know 

 of the habits, geographic distribution, and ecology of other geocarpic 

 and amphicarpic species. Whether the water storage cells of the leaflets 

 play a functional role in this complex of factors is unknown. 



