Heterostyled Flowers 411 



hybrids 1 , with which their behaviour in other respects, as Darwin 

 showed, presents so close an agreement. This view receives support 

 also from the fact that descendants of a flower fertilised illegitimately 

 by pollen from another plant with the same form of flower belong, 

 with few exceptions, to the same type as that of their parents. 

 The two forms of flower, however, behave differently in this respect. 

 Among 162 seedlings of the long-styled illegitimately pollinated 

 plants of Primula officinalis, including five generations, there were 

 156 long-styled and only six short-styled forms, while as the result of 

 legitimate fertilisation nearly half of the offspring were long-styled 

 and half short-styled. The short-styled illegitimately pollinated form 

 gave five long-styled and nine short-styled ; the cause of this difference 

 requires further explanation. The significance of heterostyly, whether 

 or not we now regard it as an arrangement for the normal production 

 of hybrids, is comprehensively expressed by Darwin : "We may feel 

 sure that plants have been rendered heterostyled to ensure cross- 

 fertilisation, for we now know that a cross between the distinct 

 individuals of the same species is highly important for the vigour and 

 fertility of the offspring 2 ." If we remember how important the 

 interpretation of heterostyly has become in all general problems as, 

 for example, those connected with the conditions of the formation of 

 hybrids, a fact which was formerly overlooked, we can appreciate 

 how Darwin was able to say in his autobiography : " I do not think 

 anything in my scientific life has given me so much satisfaction as 

 making out the meaning of the structure of these plants 3 ." 



The remarkable conditions represented in plants with three kinds 

 of flowers, such as Lythrum and Oxalis, agree in essentials with those 

 in Primula. These cannot be considered in detail here ; it need only 

 be noted that the investigation of these cases was still more laborious. 

 In order to establish the relative fertility of the different unions in 

 Lythrum salicaria 223 different fertilisations were made, each flower 

 being deprived of its male organs and then dusted with the appropriate 

 pollen. 



1 When Darwin wrote in reference to the different forms of heterostyled plants, "which 

 all belong to the same species as certainly as do the two sexes of the same species " (Cross 

 and Self fertilisation, p. 466), he adopted the term species in a comprehensive sense. 

 The recent researches of Bateson and Gregory ("On the inheritance of Heterostylism 

 in Primula"; Proc. Roy. Soc. Ser. B, Vol. lxxvi. 1905, p. 581) appear to me also to 

 support the view that the results of illegitimate crossing of heterostyled Primulas corre- 

 spond with those of hybridisation. The fact that legitimate pollen effects fertilisation, 

 even if illegitimate pollen reaches the stigma a short time previously, also points to this 

 conclusion. Self-pollination in the case of the short-styled form, for example, is not 

 excluded. In spite of this, the numerical proportion of the two forms obtained in the 

 open remains approximately the same as when the pollination was exclusively legitimate, 

 presumably because legitimate pollen is prepotent. 



2 Forms of Flowers, p. 258. 3 Life and Letters, Vol. i. p. 91. 



