which the pollen of
the long-styled form reaches the stigma of the same type of flower and,
similarly, by cross-pollination in the case of the short-styled flowers.

The applicability of the terms legitimate and illegitimate depends, on
the one hand, upon the fact that insects which visit the different forms
of flowers pollinate them in the manner suggested; the pollen of the
short-styled flowers adhere to that part of the insect's body which
touches the stigma of the long-styled flower and vice versa. On the
other hand, it is based also on the fact that experiment shows that
artificial pollination produces a very different result according as
this is legitimate or illegitimate; only the legitimate union ensures
complete fertility, the plants thus produced being stronger than those
which are produced illegitimately.

If we take 100 as the number of flowers which produce seeds as the
result of legitimate fertilisation, we obtain the following numbers from
illegitimate fertilisation:

Primula officinalis (P. veris) (Cowslip)... 69 Primula elatior
(Oxlip).................... 27 Primula acaulis (P. vulgaris)
(Primrose)... 60

Further, the plants produced by the illegitimate method of fertilisation
showed, e.g. in P. officinalis, a decrease in fertility in later
generations, sterile pollen and in the open a feebler growth. (Under
very favourable conditions (in a greenhouse) the fertility of the plants
of the fourth generation increases--a point, which in view of various
theoretical questions, deserves further investigation.) They behave in
fact precisely in the same way as hybrids between species of different
genera. This result is important, "for we thus learn that the difficulty
in sexually uniting two organic forms and the sterility of their
offspring, afford no sure criterion of so-called specific distinctness"
("Forms of Flowers", page 242): the relative or absolute sterility
of the illegitimate unions and that of their illegitimate descendants
depend exclusively on the nature of the sexual elements and on their
inability to combine in a particular manner. This functional difference
of sexual cells is characteristic of the behaviour of hybrids as of the
illegitimate unions of heterostyled plants. The agreement becomes
even closer if we regard the Primula plants bearing different forms of
flowers not as belonging to a systematic entity or "species," but as
including several elementary species. The legitimately produ