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322 ON A NEW HYBRID POTAMOaETON OF TIIS FLUITANS GROUP.
able to flower in the sliallow ditcli in which it grows. This ditch
has been carefully examined for water-plants by me for some years
past, but no Jliiitaus-iorms were detected until the present season,
when I was surprised at finding numerous young plants, apparently
seedlings in their second year. As I at once saw by the thickly
coriaceous lower leaves that these young plants belonged to 1'.
crdssifulius, I carefully examined the vegetation of the whole ditch,
which then contained water only two or three inches deep along its
whole course. At the upper end a single patch of P. natuns grew
with here and there a plant of P. plantdi/ineiis, but neither of these
species was in flower, nor pushing up flower-spikes. About fifty
yards lower down the ditch 1'. Zizil became very abundant and
flowered freely, and amongst this species I found a single plant of
P. natans, which had spread out into a small patch, showing it had
occupied that station for some three or four years : immediately
below this, and for the distance of 00 or 70 yards, single young
plants of P/crassifolkts grew ; they were not scattered irregularly
over the bottom of the ditch, but grew on one side of it, just where
the flow of the water would carry the seeds when the drainage-mill
was at work. Now this ditch for some years has been completely
isolated from the main drain, into which it flows, except by a
narrow tunnel at the end of the ditch, through which no fragments
of plants or seeds could easily pass. No plants of crassifolius were
found at this lower end of the ditch, so it was evident that they
had not been introduced from the main drain. At this lower end
a few dwarf plants of P. luccns were growing, but the water was too
shallow, and had been for some years, to allow them to flower
besides, the plants oi crassifolius did not grow near the lucens plants,
and there is no upward flowing of the water to have carried their
seeds to where the plants of crassifolius grew, even if they had been
able to flower.
I have been thus minute in describing this locality, because it
affords one of the strongest proofs of natural hybridity in Potamogetons
that it is possible to meet with. So thoroughly had this
particular ditch been examined by me for some years past that I
can safely affirm that these seedUngs did not exist before the
summer of last year, when they would naturally be too small to
attract attention.
Hitherto I had found it difficult to understand how a whole spike
of flowers could become fertilised by the pollen of another species of
Potam