- 273 — 



That P. fluitans auct. encompasses two quite different forms 

 is easily proved by means of anatomy; each of the two forms 

 even belongs to each of the two groups founded by me. According 

 to the only distinction hitherto used, we might call the one form 

 „the barren" and the other „the fruiting" or the Neckar 

 plant, because the river of Neckar is the place from where this 

 plant is best known and from where I have happened to examine 

 live materials. 



Fig. 8. P. lucens X nutans; transverse section of the stem (c. 23: 1); 

 h, epidermis; Ik, lacunae, d, wall between the lacunae; s, subepidermal bast 

 bundles; s M bast bundles in the bark: k, vascular bundles; cs, the axial cylinder: 

 the hatched parts = pith ; the white parts = vascular bundles ; the black 

 parts = mechanical tissue. 



The barren form, the only one which has been found in 

 Denmark, must be reckoned to the P. amplifolius-grouip, if we want 

 to class it into the above given system ; in the structure of the 

 axial cylinder, however, it often approaches to the P. lucens-growp 

 which is simply because the barren form is certainly a bastard 

 between P. lucens and P. natans. If only we stick to the charac- 

 ters here used, the barren form shows the following facts: In the 

 bark of the stem are numerous bundles (Fig. 8), in part some 

 rudimentary, with bast surrounded vascular bundles; in part and 



