OX A NEW HYBRID POTAMOGETON OF THE FLUITANS GROUP. 825 



' Icones,' f. 88. But by also admitting such a plant a P. Illinoensis 

 Morong as equal to P. fluitans Roth, it is evident that in this instance 

 he takes an extremely wide view of the term "species," since P. 

 Illinoensis is a form which might very well pass for a variety of P. 

 coriaceus. 



After having carefully compared the very beautiful and com- 

 plete specimens from the Neckar, in Dr. Tiselius' herbarium, with 

 a fine series of Swedish and British forms (which exactly agree with 

 the description of Roth and the figure of Reichenbach), I am unable 

 to regard them as belonging to the same species. If we are to 

 admit such forms as the Neckar plant and P. Illinoensis of Morong 

 to he fluitans-iovms, then we ought also to include in the same group 

 such plants as P. coriaceus and the large deep-water forms of P. 

 polygonifolius, a length which few botanists would feel disposed to go. 



How far Dr. Tiselius and I agree about the true nature of 

 P. fluitans, as figured in the ' Icones,' may be seen by the following 

 extract from a recent letter, which I have his kind permission to 

 publish: — "In the case of P. fluitans Roth, it has sometimes 

 occurred to me that P. fluitans might be P. natans x P. lucens, but 

 the remarkable thing about that hybrid would then be that it is 

 never difficult to distinguish it from its parents as are the hybrids 

 of nitens, of g ram incus, &c. In this country the plant is no longer 

 found growing in but one place, i. e., WaUstanas, where I recently 

 found it. How did it come thither ? Possibly brought by birds ? 

 Certainly both natans and lucens grow there, but no form of fluitans 

 can be taken for natans or lucens. In this country fluitans is not found 

 with fruit, but, as you have probably noticed, I did find it with 

 fruit, somewhat developed, in the Neckar, and believe I know the 

 plant well. In the localities where it was formerly found in this 

 country it has died out for the past fifty years ; I can take young 

 wild specimens, in every respect similar to the cultivated ones you 

 were so good as to send me, in abundance at WaUstanas. It is a 

 remarkable plant which, it seems to me, must be looked at as a 

 species, in the sense that, as you remark, many a plant now con- 

 sidered as being a species was originally an hybrid, and that in 

 process of time hybrids can produce fertile plants. Our cold climate 

 and water may be the reason that the leaves rot away before any 

 fruits have time to grow. The spikes seldom rear themselves above 

 the water, because here at WaUstanas the plant is drawn down by 

 running water, but that is no proof that the plant cannot produce 

 ripe fruit, since fertilisation can go on under water, as, for instance, 

 in the case of P. mannus, which, in this country, never rears itself 

 above the water, but nevertheless produces abundance of ripe 

 fruits" (Dr. Gustaf Tiselius in litt. July 14th, 1890). Taking the 

 plant of the 'Icones' as the type of P. fluitans Roth, I would place 

 under it the Swedish plant from WaUstanas and the British plants 

 gathered by Mr. W. II. Beeby in Sussex (1880) and in Surrey 

 (1880), and those gathered by myself in Huntingdonshire (1881) 

 and m Cambridgeshire (1885). This form is also found in many 

 continental localities, as far as one can judge from the very 

 insufficient specimens usually distributed by collectors. 



