MODIFICATION OF THE ORGANS OF PLANTS 75 



Lathyrus Aphaca. The foliage leaf (fig. 4, leaves 

 4 and 5), which most nearly resembles the primi- 

 tive type, 1 consists of two stipules and a petiole 

 which terminates in a point and is provided with a 

 pair of lateral leaflets. 



Each individual plant is furnished with from one 

 to three of these foliage leaves. 



Above them are leaves (fig. 41, leaf 6) consisting 

 of only a hypopod which forms two large stipules 

 that partially enclose a small point arising from 

 the epipod. The entire function of assimilation is 

 exercised by these stipules, and consequently both 



(/) Finally, there are some scaly leaves which also consist 



merely of a hypopod. These protect the tubers (fig. 



40, A), and are practically devoid of chlorophyll. These 



various leaves follow one another in the course of the 



growth of the plant, in the inverse order to that in 



which they are here described. As winter approaches, 



some upright stems appear, the inflated ends of which 



are stored with reserve nutrition (fig. 40, A). It is 



round these tubers that the scaly leaves are to be found. 



The bud which does not develop until the following 



Spring is at the top, surrounded by folded leaves. The 



ribbon-like leaves which grow under wa-ter and also those 



broadened out at the ends make their appearance in the 



course of the Summer. Next come the floating leaves 



with slightly developed barbs, then the leaves which rise 



well above the surface of the water, and finally the scaly 



leaves which grow out of the flowering stalk. 



1 The foliage leaves of Lathyrus Aphaca may be regarded as the 



best representatives of the primitive leaf, for in most species of 



the genus Lathyrus, each leaf is furnished with leaves and with 



one or more tendrils. L. Aphaca is probably specialized from 



other species, for the majority of the leaves have lost their lateral 



leaflets. 



