— i7G — 



altered but in return it becomes c[uite clear; for F. fluitans f. 

 stagnatilis and the Neckar- plant turn out to belong just to one 

 and the same species of the P. j^olyc/onifolius-gvoup, and because 

 of that Sch wendener's determination of the plant may be the 

 right one; but at the same time it becomes quite clear that his 

 conclusion about the influence of rapid waters on the development 

 of bast is, at least on this point, untenable or rather: the supposi- 

 tion is wrong, for in this case it is not the rapid waters 

 that cause the difference between the two forms but 

 the fact is, that we have here to do with two systema- 

 tically quite different plants each of them belonging to 

 its own group: the one o f t h e m without and the other 

 one with bast- and vascular bundles in the bark. 



As to the barren form of P. fluitans, it is generally supposed 

 to be a bastard, namely P. htcens x natans which by means of 

 anatomy I have tried to prove (1. c. page 97 — 98). hi P. natans, 

 P. lucens and in the bastard too numerous bundles are present in 

 the bark, and the endodermis is decidedly a G-endodermis. With 

 regard to the structure of the axial cylinder of the bastard it 

 resembles more or less that of P. natans or that of P. lucens. 

 Though the bastard as a rule has very long and often more than 

 metre long, vigorous shoots, the axial cylinder is never as big as 

 it is in P. natans. The vascular bundles of the bastard are often 

 quite separated as are the vascular bundles of P. natans, the sepa- 

 rating pith, however, is much smaller in the bastard. In some 

 individuals the vascular bundles are meeting in three groups cor- 

 responding to the three bundles in P. lucens, and the transverse 

 section is more oblong as in this. Finally you will find individuals 

 of the bastard with the two large bundles in front of the middle 

 of the two long sides of the section wholly united and with a 

 common large channel in the middle closely resembling that of 

 P. lucens. The bundles in the ends of the section are most usually 

 also united, however not so closely as by P. lucens also the chan- 

 nels of the single bundles are still separated from each other. 



Here must be added, however, that hardly all barren individuals 

 diagnosed as P. fluitans belong to P. lucens x natans; it is most 

 likely that certain other bastards, especially P. gramineus x natans 

 and P. alpinus x lucens, have sometimes been classed as P. fluitans. 



Hence it must be taken for granted that P. fluitans auct. in- 

 cludes two quite different plants viz., 1) an independent species 



