272 



the leaf is more short-stalked than that of the latter. The 

 epidermis of the upper surface consists in part of very distinctly 

 transversely elongated cells with slightly undulating lateral 

 walls. The outer walls are 6— 8/^ thick, with distinct cuticle. 

 The stomata occur in fair numbers (not so abundantly, however, 

 as upon the foliage-leaves), and scattered evenly over the whole 

 surface from the apex to the base. At the apex of the leaf 

 there is a hydathode with convex epithema. So far I could 

 see, the stomata, both upon the leaf-blade itself and upon the 

 epithema (the water-pores). Fig. 20, are functionless, the middle 

 lamella in the wall common to both guard-cells not appearing 

 to part, so that even upon the oldest leaves the stomata are 

 permanently closed. 



The epidermis of the lower surface consists of elongated 

 cells, longer than those upon the upper surface. Outer walls 

 6 — H fj. in thickness; cuticle present and stomata absent. Along 

 the margin are glandular hairs, precisely similar in structure 

 to those of the foliage-leaves. 



The veins and the hydathode are exactly similar to those 

 of the foliage-leaves, but — as already mentioned — upon the 

 epithema the water-pores are closed. 



The cells of the mesophyll are all more rounded than are 

 those in the foliage-leaves ; the cells of the layer answering to 

 the palisade are set obliquely to the epidermis as in 

 the foliage-leaves, although they are filled with starch- 

 grains and are without chlorophyll; so this oblique position 

 has absolutely no connection with any light-orientation 

 which may have reference to assimilation. The cells 

 of the spongy parenchyma are rounded and filled with starch. 



Consequently, in these fleshy leaves are found three struc- 

 tural features which, for the existing functions of the leaves, 

 appear to be useless rudiments inherited from parent-plants 

 with foliage-leaves similar in structure to those of the present- 

 day S. flagellaris. 



