CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 339 



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 ren- 

 dered 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 be- 

 haved 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 

 have 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 

 flowers of Viola are indeed sterile unless they are vis- 

 ited by bees; but when thus visited they yield the full 

 number of seeds. As far as I have been able to dis- 

 cover there is only one absolute exception to the rule 

 that the perfect flowers are fertile, namely, that of 



* Dr. Ascherson, 'Bot. Zeit.,' 1871, p. 555. 



