DIMORPHISM. oD 
are really sexual forms of one and the same species, 
ordinarily occurring on different plants, 7. ¢. dicecious, 
but occasionally formed on the same spike. The same 
excellent observer has demonstrated that the di- and 
trimorphic forms of Primula, of Linwm, Lythrwm, and 
other plants—forms differing maimly in the relative 
length of the stamens and styles, are also connected 
with striking differences in the number of perfect seeds 
produced. The most perfect degree of fertility is 
obtained when the stigma of one form is fertilised by 
the pollen taken from stamens of a corresponding 
height. On the other hand, when the union is, as Mr. 
Darwin states, illegitimate, that is, when the pollen is 
taken from stamens not corresponding in length to the 
style, more or less complete sterility ensues in the 
progeny, sometimes even utter infertility, ‘such as 
happens when two distinct species are crossed, so 
that, in point of fact, the offspring of these illegitimate 
unions correspond almost precisely to hybrids.’ 
Mere variations of form arising from hybridisation 
or other causes hardly fall within the lmits of this 
work, though it is quite impossible to say where varia- 
tions end and malformations begin. There are, how- 
ever, two or three cases cited by Mr. Darwin’ from 
Gallesio and Risso to which it is desirable to allude. 
Gallesio impregnated an orange with pollen from a 
lemon, and the fruit borne on the mother tree had a 
raised stripe of peel like that of a lemon both in colour 
and taste, but the pulp was like that of an orange, and 
included only imperfect seeds. Risso describes a 
variety of the common orange which produces 
“‘rounded-oval leaves, spotted with yellow, borne on 
petioles, with heart-shaped wings; when these leaves 
fall off they are succeeded by longer and narrower 
leaves, with undulated margins, of a pale green colour, 
embroidered with yellow, borne on foot-stalks without 
1 The reader will find an abstract of Mr. Darwin’s views in his work 
on the ‘ Variation of Animals and Plants,’ vol. ii, p. 181. 
2 Loc. cit., 1, 336. 
