308 



between "submerged" and "emerged" leaves, between which how- 

 ever as above mentioned, the boundary should not be drawn defin- 

 itely at the surface, in any case not in Denmark. These ribbon- 



Fig. 5. Hippuris vulgaris L (X ca. 4). 



a, 6, с lower leaves, d submerged ribbon-leaf, e upper leaf. 



leaves have no lateral veins, but have hydathodes or they are 

 emarginated after the tip is thrown off (fig. 6 d). On transverse 

 sections of them which were examined, only one row was seen 



a. b. с 



Fig. 6. Hippuris vulgaris L. (x ca. 200). 



a apex of leaf with hydathodes. b, с stomata, 6 from upper leaf, с from ribbon-leaf. 



of large chlorophyll cells between the epidermis of the upper 

 and under sides, which is said to be common by Schindler 

 (1904 p. 75). Some Danish ribbon-leaves had three (cf. Clements 



