94 MB. C. DAKWI^' ON THE DIMOHPHIC CONDITION 



lips, but t'urtber experiments are absolutely necessary. We may 

 also suspect that the fact noticed by florists*, that the varieties 

 of the Polyanthus never come true from seed, may be in part 

 due to their habitually crossing with other varieties of the Poly- 

 anthus. 



The simple fact of two individuals of the same undoubted species, 

 when homomorphically united, being as sterile as are many distinct 

 species when crossed, will surprise those who look at sterility as a 

 special endowment to keep created species distinct. Hybridizers 

 have shown t that individual plants of the same species vary in 

 their sexual powers, so far that one individual will unite more 

 readily than another individual of the same species with a distinct 

 species. Seeing that we thus have a groundwork of variability in 

 sexual power, and seeing that sterility of a peculiar kind has been 

 acquired by the species of Primula to favour intercrossing, those 

 who believe in the slow modification of specific forma will natu- 

 rally ask themselves whether sterility may not have been slowly 

 acquu-ed for a distinct object, namely, to prevent two forms, whilst 

 being fitted for distinct lines of life, becoming blended by marriage, 

 and thus less well adapted for their new habits of life. But many 

 great difiicultiea would remain, even if this view could be main- 

 tained. 



Whether or not the dimorphic condition of the Priinula has 

 any bearing on other points in natural history, it is valuable as 

 showing how nature strives, if I may so express myself, to favour 

 the sexual union of distinct individuals of the same species. The 

 resources of nature are illimitable ; and we know not why the 

 species of Primula should have acquired this novel and curious aid 

 for checking continued self-fertilization through the division of the 

 individuals into two bodies of hermaphrodites with different 

 sexual powers, instead of by the more common method of the 

 separation of the sexes, or by the maturity of the male and female 

 elements at difi'erent periods, or by other such contrivances. Nor 

 do we know why nature should thus strive after the intercrossing 

 of distinct individuals. We do not even in the least know the final 

 cause of sexuality ; why new beings should be produced by the union 

 of the two sexual elements, instead of by a process of partheno- 

 genesis. When we look to the state in which young mammals 

 and birds are born, we can at least see that the object gained is 



» Mr. D. Beaton, in ' Journal of Horticulture,' May 28, 1861, pp. 154, 244. 

 t Giirtncr, Bastarderzeuguiig, s. 165. 



