340 CONCLUDING REMARKS CHAP. VIII. 



flowers being irregular, one genus alone out of the 38 

 heterostyled genera described in the previous chapters 

 bears such flowers ; yet all these genera are absolutely 

 dependent on insects for their legitimate fertilisation. 

 I know not how to account for this difference in the 

 proportion of the plants bearing regular and irregular 

 flowers in the two classes, unless it be that the hetero- 

 styled flowers are already so well adapted for cross-fer- 

 tilisation, through the position of their stamens and 

 pistils and the difference in power of their two or 

 three kinds of pollen, that any additional adaptation, 

 namely, through the flowers being made irregular, 

 has been rendered superfluous. 



Although cleistogamic flowers never fail to yield 

 a large number of seeds, yet the plants bearing them 

 usually produce perfect flowers, either simultaneously 

 or more commonly at a different period ; and these 

 are adapted for or admit of cross-fertilisation. From 

 the cases given of the two Indian species of Viola, 

 which produced in this country during several years 

 only cleistogamic flowers, and of the numerous plants 

 of Vandellia and of some plants of Ononis which 

 behaved during one whole season in the same manner, 

 it appears rash to infer from such cases as that of 

 Salvia cleistogama not having produced perfect flowers 

 during five years in Germany,* and of an Aspicarpa 

 not having done so during several years in Paris, that 

 these plants would not bear perfect flowers in their 

 native homes. Von Mohl and several other botanists 

 nave repeatedly insisted that as a general rule the 

 perfect flowers produced by cleistogamic plants are 

 sterile ; but it has been shown under the head of the 

 several species that this is not the case. The perfect 



Dr. Aschersou, ' Dot. Zeit.' 1871, p. 555 



