ABORTION. 4.69 
culiar conditions of cultivation; thus, cuttmmgs and 
layers produce sterile and abortive seeds much more 
frequently than plants of the same species raised from 
seed; 6. abortion of the seed is often combined with 
luxuriant development of the walls of the fruit. 
Temperature and climatal changes in general seem 
not to be without effect, as has been already mentioned 
in the case of Arenaria tetraquetra, which 1s polygamous 
when growing in mountain districts. Other illustra- 
tions of a similar character are mentioned under the 
head of Heterogamy (p. 196). 
Pressure has been already alluded to as one of the 
most obvious of the inducing causes of atrophy and 
suppression. 
In the case of Ranunculus auricomus before cited, in 
which the petals are rarely perfect, M. de Rochebrune 
considers that the deficiencies in question depend, in 
great measure, on the amount of moisture in the 
localities where the plant grows. In most places the 
flowers and carpels are apt to become more or less 
abortive, while the leaves are luxuriant; while, in dry 
places, the foliage is small, but the flowers are more 
perfect. This is quite consonant with other facts relat- 
ing to the development of flowers or of leaves in general. 
But while external agencies undoubtedly play some 
part in bringing about these changes, it 1s almost cer- 
tain that internal causes inherent to the organization 
of the plant are more important. Mr. Darwin’ accounts 
for the existence of rudimentary organs by the opera- 
tion of the general rule of inheritance, and explains their 
stunted condition as the effect of disuse, not so much, of 
course, in the particular flower as in its predecessors. 
This disuse may be the result of the superior efficacy 
of foreign pollen as contrasted with that formed in the 
individual flower itself. In this way many hermaphro- 
dite flowers tend to become dicecious, as in Caryophyl- 
lacee, Orchidacee, Plantaginacee, Primulacee and other 
orders. 
1 «Origin of Species,’ p. 450. 
