198 
R. H. Compton. 
Of two species of the same genus one may be self-fertile the 
other self-sterile, as in the case of Corydalis luted. and C. cava 
respectively. LiYium bulbiferum is self-sterile, but the sub-species 
L. Buchenavii is self-fertile (Jost 1907). Kirchner (1905) has 
shown that on the whole the perennial members of the Leguminosae 
are self-sterile, the hapaxanthic self-fertile. Certain cultivated 
varieties of Plum ( Primus domestica) and Cherry (P. cerasus) are 
highly self-sterile (with slight parthenocarpy, i.e., growth of the fruit 
though not of the seed), others self-fertile (Backhouse, 1911). 
Some individuals or races of a species may be highly self-sterile ; 
others, taxonomically indistinguishable, self-fertile. This is the case, 
for instance in Reseda odorata (Darwin, 1876): and apparently also 
in the Tunicate Ciona ifitestinalis, which Castle and Morgan (1905, 
1910) find to be self-sterile in America, but which Potts (1910) finds 
self-fertile at Naples. On the other hand a change in environment 
may produce a marked effect: as in the cases of Eschscholtzia cali- 
tornica and Abutilon darwinii , self-sterile in their native Brazil but 
moderately self-fertile in England (Darwin, 1876). Passijlora alula 
is said to have been rendered self-fertile by being grafted on a 
distinct species. Biophytnm sensitivum is said to be self-sterile in 
its open, self-fertile in its cleistogamous flowers. It is probable that, 
in some cases of partial self-sterility, geitonogamy produces more 
seeds than autogamy though less than xenogamy. 
Further, the degree of self-sterility varies enormously. In a 
great many cases the offspring of a self-pollination are slightly fewer 
than those of a cross-pollination : 1 at the other extreme there are 
a few cases in which the stigma and pollen of the same flower are 
mutually poisonous. 
Clearly there are very many problems awaiting solution with 
respect to the causation of self-sterility and the reasons for its 
apparently capricious incidence. 
II.— Causation of Self-Sterility. 
From the standpoints of Chemistry and Morphology there is 
the problem of the exact nature of the hindrance to self-fertilisation. 
1 The offspring of a self-pollination are often not merely fewer but weaker 
than those produced by a cross. This is probably a different phenomenon from 
that of the evil (or good) effects arising from in-breeding, which it is customary 
to explain as due to the increased chance of the meeting of similar recessive 
characters in consanguineous matings. Nor is it a phenomenon of self-sterility 
in the strict sense, for fertilisation occurs: but it may be suggested that the 
incompatibility between paternal and maternal tissues which brings about the 
failure of a percentage of fertilisations may also apply as between the paternal 
and maternal portions of the protoplasm in each cell of the zygote, and that 
weakliness of constitution is the result. 
