— 275 — 



the barren form, having a circle of c. 8 always quite separated 

 vascular bundles. On the transverse section of the petiole only a 

 number of rather large vascular bundles are to be seen lying in a 

 bowed line, and no scattered bastbundles or rudimentary vascular 

 bundles appear. These characters in connection with the fact that 

 this plant is endowed with both floating leaves and submerged 

 leaves, make us class it into the P. polygonifolius-group which is 

 remarkable just for the lack of bundles in the bark of the stem 

 and consequently has nothing to do with neither the P. natans- 

 nor the P. lucens- or the P. amplifolius-group, all of them having 

 numerous bundles in the bark. Hence there is no room neither 

 for Ascherson & Graebner's hypothesis. 



Here I shall refer to a fact I have mentioned before (I.e. page 98), 

 but that now for the first time has its explanation. As is said 1. c, 

 Schwenden er 1 ) speaks of one in quiet waters living form of P. 

 fluitans viz. P. fluitans var. stagnatilis Koch that is quite without 

 bundles in the bark, and on this fact Schwendener founds his 

 opinion that the pull of current waters adds to the development 

 of bast bundles. On account of this I wrote (I.e. p. 99): „A series 

 of years ago I transplanted several individuals of the form sub- 

 natans 2 ) from very rapid waters in the Varde rivulet into the 

 botanical garden's water basins, but these individuals have an 

 unaltered strong growth of the bast bundles, as those have which 

 are developed in the rivulet. It is then to be supposed that 

 Schwendener's statement about P. fluitans f. stagnatilis is founded 

 upon a wrong definition. All individuals I have examined of P. 

 natans and P. lucens and of the bastards between the two had 

 numerous bundles in the bark, while, as before said, P. polygoni- 

 folius, P. coloratus and P. alpinus are without both vascular bundles 

 and bast bundles. Most likely then Schwendener's P. fluitans f. 

 stagnatilis is nothing but large and long-leaved individuals of P. 

 polygonifolius, that is not uncommon and which in appearance is 

 very much like P. fluitans, and now and then is mistaken for 

 this one". 



At the time I wrote this, I only knew the barren form of P. 

 fluitans viz. P. lucens x natans. Since I have seen and examined 

 the fruiting form viz. the Neckar-plant, the case is somewhat 



') Schwendener, S., Das mechanische Princip im anatomischen Bau der 



Monocotylen, page 122. 

 2 ) o: the barren form of P. fluitans. 



