— 255 - 



Hoping that other botanists who are within reach of material 

 of foreign species will either themselves examine it anatomically or 

 send it to me for examination, I shall publish here the principal 

 results of my investigations especially in so far they concern a 

 group-division of species founded upon anatomical characters. 

 Moreover I shall give a single example testing the value of the 

 anatomical characters employed when used for the examination of 

 the single species, and show that by aid of those characters the 

 question „what is Potamogeton fluitans Roth" which for such a 

 long time has so greatly puzzled the Potamogeton-judges, is easily 

 settled. 



I. 



Anatomical contributions to a Monograph of 

 the genus Potamogeton. 



As already stated I have in the following synopsis considered 

 only characters that are to be had from the stem and the leaves, 

 and of those characters again I have only used such that were 

 most marked and most practicable because it is here more impor- 

 tant to find a practical principle for division than to give contribu- 

 tions to a thorough description of the species. 



As to the stem I beg to observe that the structure of the top 

 of it viz. the peduncle differs widely from the structure of the 

 other parts of the stem. Hence we look at the stem apart from 

 the peduncle and especially so because the individuals are often 

 without flowers and peduncle. As far as I have seen the other 

 parts of the stem are mainly uniform as to the characters fit for 

 use. For safetys sake, however, it is to be noticed that the charac- 

 ters employed are as a rule from sections taken near the middle 

 of the stem's upper half, which part of the plant you will most 

 often have before you. 



On the transverse section of the stem of monocotyledoneous 

 land plants the scattered vascular bundles are arranged as is well 

 known especially near the circuit of the stem. At the Potamogeton, 

 on the contrary, as by many other aquatic plants, all the vascular 

 bundles or at least many of them are more or less close together 

 in the middle of the stem forming an axial cylinder that is sharply 

 bounded from the bark outside. The biological explanation of this 

 difference between land plants and aquatic plants may be drawn 



17* 



