321 



Äs the anatomy of aquatic-plants varies exceedingly within 

 the species, influenced as they are by the very variable con- 

 ditions to which they are exposed, no great importance should 

 be attached to these smaller ditïerences, the value of which 

 can not be measured without intimate 

 knowledge of local conditions. 



As is quite natural, because of the 

 more intense assimilation, in some cases 

 much more starch is found in the short 

 and broad leaves than in the narrow leaves, 

 often quite filling up the chlorenchyma 

 cells of the former. 



Fig. 17. Callitriche 

 hamulata (X ca. lt>5). 

 Callitriche develops flowers and fruits Transverse section, middle 



of leaf. Starch is seen. 



in abundance in arctic countries; only a 



few specimens of the material are devoid of flowers. Both are 



found at the same time generally, except of course in the 



beginning of the summer, when only the very first flowers are 



present. 



Greenland I Iceland 



only flowers fruiting only flowers fruiting 



The flowering period is thus in the main as was to be 

 expected, somewhat later than in temperate regions. Very 

 likely fruits and perhaps flowers might be found later in the 

 year than Aug. — Septb., but as mentioned before, most travellers 



