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SUPPOSED HYBRIDITY IN POTAMOGETON. 175
produced floating leaves, but gradnally extended itself year by year
until it began to form a little colony or bed sufficiently strong to
keep out other forms of the genus from intruding on its territory.
Its exact station was sufficiently fixed in my memory by the fact
of its occupying a clear space of water between two local forms of
P. Zizii and P. heteroplujllus. In June of 1889 I visited this drain
for the first time that season, and was greatly surprised to see a
new form of Potamorjeton quite unknown to me. I thought I knew
each individual plant in Broker's Drain as well as I knew each individual
face in the circle of my friends, for I had watched and
gathered specimens of each local form and of almost every individual
plant for four or five years, yet here was something quite new
and which I could not refer to any segregate known to me.
Hastily fishing a plant up, the lower leaves of the stem at once
showed that it was the supposed seedling I had referred to P.
fuctuans. The next point was to make sure of the exact locality
by examining the plants on either side, and I found the beds of
Zizii and heteropJnjIlus, both of which I know perfectly well. Now
this new form of P. jluctiians was not like the other forms I had
referred to this segregate, except in the lower leaves, but was
curiously intermediate between the local forms of P. Zizii and
P. heteroplujllus which grew on either hand. Perhaps it is hardly
possible to obtain a stronger proof of a natural hybrid or crossbred
plant than this instance affords. It seems to me only less
strong than would be the case if such a form had been obtained
artificially, by actually crossing the Zizii and heterophylhis-iovms.
Unfortunately the drain was cleared of weeds in the ensuing wet
July, before the plant had time to produce fruit, which, I think, from
the appearance of the abundant flower- spikes, it would have done.
The origmal Scandinavian form, named by Dr. Tiselius, " P.
heterophi/lliis Schreh. V. jiuctuans mihi," certainly fruits readily. I
have always considered it to be a hybrid between hcterophyUm and
Zizii, approaching more nearly the former plant. I sent Dr. Tiselius
one of the forms from Broker's Drain, labelled '' heterophyllus x
^un," on which his comment is, " resembling /Hcfua?isTis.," . . .
" possibly Zizii x hcterophijllus (as) observed by you." This second
Jhu'tiuDis-fovm. fruits freely with us, but perhaps less so than either
of its supposed parents.
Having thus convinced myself that these two forms, P. Zizii and
P* lietcropJiijllMs, do interbreed, I next turned my attention to the
local circumstances in which /-*. varians grows, and to the variations
it undergoes, both independently of, and in connection with, those
conditions. I had previously suspected the hybrid origin of P.
raridiis, as my published note on that segregate will show,* but now
I began to push my resciirches in a fresh direction with some degree
of confidence. This was to observe whether any variation had
resulted from propagation by seed, or otherwise, in a colony of P.
varians whicli grew apart from botli Zi:ii and liftewphyllu^, and
ofi'ered an unusually favourable opportunity of seeing what a single
plant of a supposed hybrid would do when left to itself.
• Journ. Bot. 1889, 35.