ABORTION. 469 



culiar conditions of cultivation; thus, cuttings 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 is 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 Bammculus auricomus before cited, in 

 which the petals are rai'ely perfect, M. de Rochebrune 

 considers that the deficiencies in question depend, in 

 great measure, on the amount of moisture in the 

 locahties 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 is 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 dioecious, as in Caryophyl- 

 lacece, Orchidacece, Plantaginacecey Pnmulacece and other 

 orders. 



* ' Origin of Species,' p. 450. 



