410 The Biology of Flowers 
reaches the stigma of the short-styled form or if pollen of the short- 
styled flowers is brought to the stigma of the long-styled flower, that 
is the organs of the same length of the two different kinds of flower 
react on one another. Illegitimate fertilisation is represented by the 
two kinds of self-fertilisation, also by cross-fertilisation, in 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 versd. 
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) wi eee 
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 genera- 
tions, sterile pollen and in the open a feebler growth’. 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 dis- 
tinctness?”: 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 produced plants are thus true 
1 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. 
2 Forms of Flowers, p. 242. 
