Page:Journal of botany, British and foreign, Volume 34 (1896).djvu/18

 2 POTAMOGETON NITBNS WEB. 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 different 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 P. nitens lies in the abundantly de- veloped coriaceous flouting 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 :— 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. 189. '' P. tiatans /3. Linn. Spec. Plant, i. p. 18'2. '* Misit simile specimen Upsaliae lectum cl. Ehrhard sub nomine varietatis Pot. lucentis. A lucente autem quam maxime differt foliis oppositis, multo brevioribus (G. H. Weber, Supp. Flor. Holsat. 1887, pp. 5, 6)." Much of this description agrees very well with our plant, which is a true nitens-ioTm, although distinct in some respects from any hitherto described. Dr. Tiselius writes (in litt. July 9th, 1895) : — 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. gramineus 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- phyllus and P. Zizii, and closely resembles the specimens a. and b., No. 44, in Dr. Tiselius's Pot. Suec. Exsicc."^' 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 varians, and d. and e. on the same sheet appear to me to be shallow-water forms of the same species, Cambridgeshire specimens exactly match all th$se.
 * Potamogeton nitens. P. foliis lanceolatis oppositis Web. in fossis
 * Your P. nitens f. involuta is very beautiful ; it seems, however, to
 * c. and/, on this sheet are Hke the land-forms I have described under P.