Heterostyled Flowers 411 
hybrids’, 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?” 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*.” 
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. 
* 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. txxv1. 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. 1. p. 91. 
