342 CONCLUDING EEMAEKS Chap. VIII. 



two states on the same plant, in Viola, Oxalis, Biophy- 

 tum, Campanula, &c. In the several species of Viola 

 the various parts of the flowers have also been modified 

 in very different degrees. . Those plants which in their 

 own country produce flowers of full or nearly full size, 

 but never expand (as with Thelymitra), and yet set 

 fruit, might easily be rendered cleistogamic. Laihyrus 

 nissolia seems to be in an incipient transitional state, 

 as does Drosera Angliea, the flowers of which are not 

 perfectly closed. There is good evidence that flowers 

 sometimes fail to expand and are somewhat reduced 

 in size, owing to exposure to unfavourable conditions, 

 but still retain their fertility unimpaired. Linnaeus 

 observed in 1753 that the flowers on several plants 

 brought from Spain and grown at Upsala did not 

 show any corolla and yet produced seeds. Asa 

 Gray has seen flowers on exotic plants in the North- 

 ern United States which never expanded and yet 

 fruited. With certain English plants, which bear 

 flowers during nearly the whole year, Mr. Bennett 

 found that those produced during the winter season 

 were fertilised in the bud ; whilst with other species 

 having fixed times for flowering, but "which had 

 been tempted by a mild January to put forth a few 

 wretched flowers," no pollen was discharged from the 

 anthers, and no seed was formed. The flowers of 

 Lysimaehia vulgaris if fully exposed to the sun expand 

 properly, while those growing in shady ditches have 

 smaller corollas which open only slightly ; and these 

 two forms graduate into one another in intermediate 

 stations. Herr Bouche's observations are of especial 

 interest, for he shows that both temperature and the 

 amount of light affect the size of the corolla ; and he 

 gives measurements proving that with some plants 

 the corolla is diminished by the increasing cold and 



