176 SUPPOSED HYBRIDITY IN POTAMOGETON. 



In 1880 I found a single plant, or small patch, which had the 

 appearance of having sprung from a single rootstock, of what I then 

 supposed to be P. heterophyllus, growing in Blockmoor, near Mepal. 

 After a few years I found, on revisiting the locality, the little patch 

 had spread until it more or less covered about a hundred yards^ in 

 length of the ditch in which it grew. But the plant had now varied 

 slightly from the first gathered specimen, and I thought it to be a 

 variety of heterophyllus. Still there was nothing very striking about 

 it. In the year 1886 I noticed for the first time the plant had 

 begun to fruit somewhat freely ; the ditch having been frequently 

 dry between 1880 and 1886, probably greatly interfered, if it did 

 not entirely prevent fruiting during that period. I gathered 

 several specimens in the latter year, and found them very uniform 

 in character. The next year, however, numerous young plants, 

 apparently seedlings, began to spring up all over the ditch, pre- 

 senting an astonishing variety of forms. At this time I supposed 

 some of these forms to be P. Zizii, and others good heterophyllus, 

 while yet other forms seemed distinct from either of these plants. 



More careful study, and the discovery of P. varians, of Morong, 

 in another locality, led me to suspect this colony to consist entirely 

 of P. varians, of which a single seed or plant had been transported 

 from its head-quarters some mile or so off. (Outliers from the head- 

 quarters of a local form are frequently met with at short distances in 

 the Fen, but I know of no instance of this " accidental " transportation 

 for long distances, though it must occur at times). The identifica- 

 tion with varians proved to be correct, for our typical colony of 

 varians, named by the Rev. T. Morong himself, has since sprorted 

 by seed and extension into a similar, though less numerous, set of 

 varieties. 



Here then we have exactly the results that occur when gar- 

 deners cross Pimm satium with P. arvense, — variation by extension, and 

 variation by seed without any further cross. This Blockmoor colony 

 of P. varians sprang from a single plant, and it varied both by 

 extension and from seed just as many artificially cross-bred forms 

 do. 



Many botanists who may be inclined to think that I have fair 

 grounds for supposing that P. Zizii and P. heterophyllus do frequently 

 cross, with one another, or with Incens and the more recently 

 proposed segregates, will urge that the resulting forms are not 

 true hybrids at all but only mongrels, inasmuch as all the forms 

 under consideration are varieties of one species. This may be so ; 

 I do not hold quite the same view myself, now regarding P. lucens 

 and P. heterophyllus as not having descended one from the other, 

 but that the intermediate forms are the result of repeated crosses. 

 Whatever rank the above forms may hold, I think, however, no one 

 will regard P. nutans and P. lucens as anything but species widely 

 distinct; yet these two forms seem to cross with the result of pro- 

 ducing a plant, P. fiuitans, which is said by some botanists to be 

 occasionally fertile. As far as my observations go, the plant 

 regarded by authors as the P. fiuitans, of Both, is a barren hybrid, 

 and the fruiting form called P. fiuitans is a distinct species. Hybrids 



