32" 



As 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 differences, 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 



to ux^f l(S^/pi 

 and broad leaves than in the narrow leaves, \~\r\jj ;^t/v><-// 



often quite filling up the chlorenchyma 



cells of the former. 



Fig. 17. Callitriche 

 haniulata (X ca. 165). 



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. 



C. autumnalis. 

 C: hanmlata. 



C. stagnalis. 

 C. verna. 



Greenland 



only flowers fruiting 



Aug. 

 June— July Aug. — Septbr. 



July— Septbr. 



Iceland 



only flowers fruiting 



July 

 June— July— Aug. 



January 



July— Aug. 

 July— Aug. 



C. autumnalis. 

 C. hamulata. 

 C. stagnalis. 



C. verna. 



The Færoes 



only flowers fruiting 



July— Aug. 



July — Aug. — 



Novb. 4. 



Danmark 



flowering (Raunkiær, 1906) 



July— Septb. 

 May— Septb. 

 May— Septb. 



May — Septb. 



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

 expected, somewhat later than in temperate regions. V^ery 

 likely fruits and perhaps flowers might be found later in the 

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



