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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 roofcstock, of what I then
supposed to be P. heterophijllus, 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 heterophylliis. 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, presenting
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 fi'om 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 headquarters
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 Kev. 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 gardeners
cross Pisiim satiwnvfith P. arvense,—variation by extension, and
variation by seed without any further cross. This Blockmoor colony
of P. varians sprang fi'om 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 supposmg that P. Zizii and P. heterophyllus do frequently
cross, with one another, or with lucens and the more recently
proposed segregates, will urge that the resulting forms are not
true hybrids at all but only monyreh, 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. natans and P. lucens as anything but species widely
distinct ; yet these two forms seem to cross with the result of producing
a plant, P. fluitans, which is said by some botanists to be
occasionally fertile. As far as my observations go, the plant
regarded by authors as the P. fluitans, of Roth, is a barren hybrid,
and the fruiting form called P. fluitans is a distinct species. Hybrids