Anatomical Potamogeton-Studies and 

 Potamogeton fluitans. 



By 



C. Raunkiær. 



Potamogeton belongs to the most difficult genera as well with 

 regard to the limitation and characterization of species and forms 

 as to the correct diagnose of individuals. This depends especially 

 on the fact that the individuals not only are as a rule differing 

 widely under different outer conditions but are also differing widely 

 in different stages of growth. The species, moreover, are often rich 

 in forms, that is: one and the same species appears in several 

 more or less strongly marked systematical units of inferior rank. 

 Lastly, several species are much disposed to the producing of 

 bastards, which are often very like the real species and varieties 

 and consequently they have often been confounded with those and 

 mixed with them. 



The characters of the floral parts, the flower and the fruit, are 

 as generally comparatively fixed but the number of those characters 

 is a rather small one, and on this point, moreover, the difference 

 between the species is often very small. The characters of the 

 vegetative parts are few and at the same time often so variable, 

 that in many cases the certain diagnose of not fruiting species has 

 hitherto been impossible. Hence it must be our task to elicit some 

 characters not used in the ordinary systematical method of orien- 

 tation, especially when they are more fixed than characters hitherto 

 used and appliable in the determination of the individuals even 

 without flower and fruit. Such characters are to be found in the 

 genus of Potamogeton in certain anatomical facts. 



While I investigated the genus Potamogeton for my work: 



Botanisk Tidsskrift. 25. Bind. 17 



