32i 



on the under side of the leaf is a big hydathode (Borodin 1870 

 p. 841 and fig. 1 — 5), developed both in air-leaves and in water- 

 leaves. 



The dorsiventral condition is distinct in the upper leaves, 

 but gradually grows very in- 

 distinct downwards, the lowest 

 leaves of submerged stems 

 are almost isolaleral. 



It need hardly be said, 

 that the outer wall of the 

 epidermis is thicker in air- 

 leaves than in water-leaves. 

 The epidermis does not contain 

 any chlorophyll as does that 

 of many other aquatic and 

 amphibious plants. The cells ^^8- l^ CallitHche hamulata Ktz. 



A one of the uppermost leaves (x ca. 5). 

 have undulating walls and are B upper, c lower epidermis of a leaf like A 



(X ca. 70). 



nearly isodiametrical in the 



short and broad leaves ; the undulation gradually grows less 



marked and at last wholly disappears, the cells becoming more 



and more oblong, as the leaves 



gradually decrease in breadth dovsn- 



wards(cf. fig. 15 and 16). The drawings 



represent cells from the middle part 



of the leaves, placed between the 



mid-vein and the border. Near the 



^ „. . , , , apex the cells are in the main shorter 

 Fig. 16. Calhtriche hamulata. 



Ktz. (X ca. 70). and the walls more undulated than 



u upper, I lower epidermis of the ^^ ^j m[(]f]\Q of the leaf, and near 



leaf fig. 12 C. 



the base they are longer and narrower 

 and often straight-walled. The cells above and below the mid- 

 vein and near the border also differ, namely, in being rather 

 long and not or only slightly undulated. 



The lower epidermis generally appears less well developed 



