36 NOTES ON PONDWEEPS. 



Zizii x heterophylh<$, &c. ; and, further, the recently discovered 

 *' type-plant " itself bore a very remarkable resemblance to P. fal- 

 catus. The results of these further comparisons are as follows : — 



Graminifolius differs from v avians by the absence of the spathu- 

 late, coriaceous, submerged autumnal leaves, and of the membranous 

 Zizii-like summer foliage ; the early state, too, is very different. 

 These early states of Potamogetons are valuable as affording indi- 

 cations of the species new forms have probably descended from, and 

 whether such forms are the result of variation or hybridization. 



From P. fal catus, the species to which P. graminifolius is most 

 nearly allied, the distinction was equally well marked. In yramini- 

 folius the lower leaves are sessile, instead of semiamplexicaul ; the 

 fruit is much larger and less freely produced, the flower-spikes 

 single, instead of in clusters, and with nearly equal, instead of 

 swollen, peduncles. Again, the early spring states widely removed 

 the two forms, and under no state can i\ graminifolius be mistaken 

 for P. nitens! On the other hand, how like falcatus and nitens are 

 to one another will be best shown by the following quotations from a 

 letter recently received from Dr. Tiselius, whose knowledge of nitens- 

 forms both in the field and in the herbarium is unequalled : — M The 

 principal reason (although, as you yourself remark, not a completely 

 convincing one) for your distinguishing your f aha tits from nitens 

 seems to me to be precisely the fully and generally developed fruits 

 on some of the specimens you sent me. But why should not these 

 specimens be specimens of nitens with fruit ? " 



Enough has now been said to show how distinct P. graminifolius 

 is from the other forms which grow under apparently similar con- 

 ditions in the neighbouring fens. But the question will be naturally 

 asked, — Why has this form, resembling in its numerous states so 

 many closely allied "varieties" or "species/ 1 not developed in 

 some instances at least into one or other of them, in a locality so 

 well adapted for the production of new quasi-specific forms ? and, 

 above all, why has it not crossed with P. Zizii, and so produced 

 some of the hybrid forms said to be so common in the fens ? It 

 eertainly has crossed with Zizii! For the explanation of the rest, 

 which does not seem to present any great difficulty, I hope to write 

 a second note on P. falcatus. Here it is enough to say I can see 

 no traces of hybridity in P. graminifolius. 



The form this note has assumed has been entirely suggested by 

 letters I have recently received accompanying parcels of Potamo- 

 getons for me to name, and by the remarks I find already written 

 on the sheets of specimens by others. Those who have made a special 

 etudy of the genus are too glad to have the opportunity of com- 

 paring specimens collected by others with their own probably more 

 extensive collections, and in unusually difficult cases to consult the 

 great public herbaria in their researches after a name ; but I repeat 

 that this is often little more than a bare name, and too frequently is 

 merely the further propagation of an old error. Let students, then, 

 take what they can get from specialists, but let them test and sift the 

 information so obtained thoroughly in the field. Often it will be 



found that serious mistakes have been made by writers of preceding 



