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SUPPOSED HYBRIDITY IN POTAMOGETON. 173
Var, TERES. C, vnlfjaris var, teres Boott, iii. 168, (1867). From
Germany northward.
Var. TURFOSA. — C. turfosa Fries, Summa, 228 (1846). C. vulgaris
var. turfosa Boott, iii. 169 (1867). Scandinavia.
Var. BRACTEOSA. C. vuhjaris var. bracteosa Bailey, Proc. Amer.
Acad. Arts and Sci. xxii. Si (1886). California. Greenland.
C. Gaudichaudiana Kuntli, which Boott makes a variety of C,
vulgaris, appears, from the little material which I have seen, to be
at least a very doubtful variety of this species, and for the present
it had probably better stand alone.
SUPPOSED HYBRIDITY IN POTAMOGETON.
By Alfred Fryer.
When I first began to study local forms of Potmnogeton in the
Fens, I was strongly prejudiced against regarding any of the
generally accepted species of authors as of possible hybrid origin,
but supposed that such species as are described in our standard
works were in all cases "good species," which especially fulfilled
the first theoretical demand of a species by being sterile with all
other species of the genus. If on rare occasions a cross ever
occurred, I held that the consequent ofl"spring was absolutely
barren, and incapable of continuing its race except by " extension "
or growth from the original plant. Indirectly, these views were,
if I remember rightly, advocated in the earlier notes of this series.
By degrees, however, the local facts that presented themselves
compelled me to regard P. decipiens as a hybrid between P. lucens
and P. perfoliatus. This conclusion, by no means hastily made,
induced me more closely to examine the local distribution and lifehistory
of other so-called species of Potamogeton, and more especially
to inquh'e into such circumstances as seemed to throw any
light on their origin, or the relationship they bore one to another.
The facts observed in the course of these investigations, and the
conclusions I have arrived at, form the substance of this note. By
stating the facts fairly, I hope to enable the reader to correct for
himself any errors of inference I may have fallen into.
In a previous note I stated that such forms as P. hctcrophyUus
and P. Zidi were as variable when growing apart as wlien growing
together. This statement was altogether erroneous. I did not then
understand the difference between states of species and varieties
of species,—between forms that are only temporary and speedily
revert to the type, and forms that are permanent, for the life of the
individual at least. But continued study of tlic living plant of one
of our most apparently variable races of P. Zidi, sliowed that this
multiform plant has no true variety, iuthe botanical sense of the word,
but that all its forms may be produced on the same rootstock, often
in a single season, or at most in the course of three or four seasons,
and that these forms arc mere states due to temporary causes, such