325 



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 isolateral. 



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 

 have undulating walls and are 

 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 down- 

 wards (cf. fig. 1 5 and 1 6). 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 

 and the walls more undulated than 



Fig. 15. CalUtriche hamulafa Ktz. 



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



В upper, С lower epidermis of a leaf like A 



(X ca. 70). 



Fig. 16. CalUtriche hamulata. 

 Ktz. (X ca. 70). 



и upper, I lower epidermis of the ,„ ^j^g ^-^^^^^ ^f ^j^g ,gj^f_ ^^^ ^^^j. 



leaf fig. 12 С 



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 



