305 



sea, nol within the arctic region strictly speaking, but still in 

 the birch region. In these stalks there are only 2 circles; the 

 fact that Hippuris was here growing in the shade of some 

 small bushes, was perhaps not without influence on the structure 

 of the stems. Transverse sections of a herbarium specimen 



Fig. 3 a. Hippuris imlgaris L. 



Transverse section of stem. From Greenland. 



of H. tetraplujlla from the Åbo district, Finland, resemble 

 the arctic. Such a structure can also be found in Danish specimens 

 in the submerged portion, whilst the emerged part after an 

 even transition is like that of other Danish plants, and these 

 two stalk-forms can be taken side by side in the same pool. 

 The following seems common in H. vulgaris: in the rhizome 

 and lowermost part of the vertical shoot many and small canals, 



