^ POTAMOGETON NITENS WER. F. INVOLUTA. 



Although the drupelets are abortive, yet they are sufficiently 

 developed to make it seem likely that in exceptional cases they may 

 ripen and reproduce the species from seed. Indeed, there is much 

 in the local distribution of the form to suggest this as actually 

 taking place. Either this is the case, or the two parent plants 

 frequently cross in dift'erent parts of the locality. Certainly the 

 local distribution does not indicate diffusion by division from a single 

 plant by winter-buds or otherwise ; many individual plants must 

 have originated from seeds. 



Perhaps the most striking difference between f. involuta and the 

 previously described forms of F. nitens lies in the abundantly de- 

 veloped coriaceous floating leaves ; these amount to as many as 

 forty or fifty on a single plant, and are rarely absent either on 

 flowering or autumnal flowerless states, and are equally abundant 

 in deep and shallow water. Probably in this respect our plant 

 resembles that originally described by Weber ; I append this 

 description, kindly sent to me by my friend Dr. Tiselius : — 



" Putamogeton nitens. P. foliis lanceolatis oppositis Web. in fossis 

 prope Nostorf. Folia remota, opposita, longe petiolata, lanceolata, 

 petiolo nonnihil longiora, integerrima, superne nitentia. Pe- 

 dunculus longus, crassiusculus. Spica multiflora. 



" Habitus P. natantis, sed planta tenera, multo minor, folia 

 angustiora. Idem tamen videtur Potamogeton foliis lanceolatis 

 oblongis, petiolis longis, Gronovii Flor. Virg. p. 139. 



" P. vatans /3. Linn. Spec. Plant, i. p. 182. 



" Misit simile specimen Upsaliaj lectum cl. Ehrhard sub nomine 

 varietatis Put. lucentis. A lucente autem quam maxime differt 

 foliis oppositis, multo brevioribus (G. H. Weber, Supp. Flor. Holsat. 

 1887, pp. 5, G)." 



Much of this description agrees very well with our plant, which 

 is a true nitens-iom\, although distinct in some respects from any 

 hitherto described. Dr. Tiselius writes {in litt. July 9th, 1895) : — 

 " Your P. nitens f. involuta is very beautiful ; it seems, however, to 

 me to be a form originating in the same way as other forms of nitens. 

 Peduncles, spikes, stipules, and stalks, are those of P. nitens, but 



the leaves are nearer to those of P. grami)ieus I do not 



think I have seen it in any herbarium, nor have I found it on the 

 Continent." 



In the summer of 1895 I found the "land-form" of our plant. 

 It is very distinct in habit from the tufted land-forms of P. hetero- 

 jihyllus and P. Zizii, and closely resembles the specimens a. and b., 

 No. 44, in Dr. Tiselius's Pot. Suec. Phvsicc* 



Beautifully and carefully as Mr. Morgan has drawn the land- 

 form, it has been impossible to adequately represent the coriaceous 

 or semicoriaceous texture of the leaves without the aid of colour. 

 The specimen figured was growing entirely oat of water, and nearly 

 every leaf was more or less coriaceous. 1 may add that, although 



* c. and/, on this sheet are like the land-forms I have described under P. 

 variriiis, and d. and e. on the same sheet api^ear to me to be shallow-water 

 forms of the same species. Cambridgeshire specimens exactly match all these. 



