306 



higher up larger and fewer, then in the upper submerged part 

 and in the aerial part again many and small, though not so 

 marked as in the rhizome. 



The outer wall of the epidermis may be rather greatly 

 thickened. The cuticle, coloured red with Sudan HI, has fine, 

 longitudinal folds (fig. 4), as can be seen both in arctic and 



Fig. 3 b. Hij)puris vulgaris L. 

 Transverse section of stem. From Denmark. 



in fresh, Danish material, where the folds of the submerged 

 part however are indistinct in some cases, 



CosTANTiN (1884 p. 317), who has investigated the propor- 

 tion between the central cylinder and bark in the air stem and 

 water stem in some amphibious plants, gives it for H. vulgaris 

 as 0,5 and 0,46; Sernander (1901 p. 170) gives for the bark 

 of the rhizome at least 5/6ths of the diameter. What the con- 

 dition in this regard is in the arctic Hlppuris has not been 



