On the Species of the Genus Primula in Essex. 163
whether this peculiarity extends to dimorphic heterostyled
species in other genera.
With Lythrum salicaria (a trimorphic species) the long-
styled plants are not the more numerous, as our member,
Mr. Gibbs, will, I understand, show in the future.
Mr. Darwin tells us that with the Cowslip and Primrose the
anthers of the two forms do not differ in size, but the pollen-
grains of the long-styled form are smaller than those of the
short-styled form in the proportion of about 70 to 100. It
follows, therefore, although I do not think he mentions the
fact, that each long-styled flower must produce about three-
tenths more pollen than each short-styled one; and as the 1. are
about one-fifth more numerous than the s., about one-half more
long-styled pollen is produced than short-styled. If, as we
shall presently see, the s. produce the most seed by about
one-fifth, it is probably that they require that amount more
pollen than the 1. to fully fertilize their ovules; but, admit-
ting this, there is still a considerable remainder of long-
styled pollen which I cannot account for, unless it is that the
stigmas of the short-styled plants, being far less exposed than
those of the long-styled plants, are less likely to receive
sufficient pollen—hence more is produced to avoid there being
any lack.
IV.—The Relative Fertility of the Two Forms in Nature.
Mr. Darwin has stated of the Cowslip that20 "the short-styled
plants produce more seed than the long-styled in nearly the
proportion of three to two: but if we take the fairest
standard of comparison, namely, the product of seed from an
equal number of umbels, the excess is nearly as four to three."
Of the Primrose he says,21 "The seeds from the short-styled
(plants) weighed exactly twice as much as those from an
equal number of long-styled plants." Now, as this seemed
to me to be directly opposed to what I have shown under
my last heading, and a most extraordinary thing that one
form of flower should produce considerably more seed, yet
the other form should be considerably more numerous, I
20 'Forms of Mowers,' p. 20.
21 Ibid, p. 36.