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 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 : 



Primtda 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 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 2 ": 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. 



