Chap. VIII. ON CLEISTOGAMIC FLOWERS. 341 



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

 fruit, might easily be rendered cleistogamic. Lathyrus 

 nissolia seems to be in an incipient transitional state, 

 as does Drosera Anglica, 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. Linnseus 

 observed in 1753 that the flowers on several plants 

 brought from Spain and grown at Upsala did not 

 show any corolla and y,et produced seeds. Asa Gray 

 has seen flowers on exotic plants in the Northern United 

 States which never expanded and yet fruited. With 

 certain English plants, which bear flowers during near- 

 ly the whole year, Mr. Bennett found that those pro- 

 duced 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 Janu- 

 ary to put forth a few wretched flowers," no pollen was 

 discharged from the anthers, and no seed was formed. 

 The flowers of Lysimachia 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 an- 

 other in intermediate stations. Herr Bouehe's obser- 

 vations 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 in- 

 creasing cold and darkness of the changing season, whilst 

 with others it is diminished by the increasing heat and 

 light.* 



* For the statement by Linnseus, xxxix. 1865. p. 105. Bennett in 

 see Mohl in 'Bot. Zeituns,' 1863, 'Nature,' Nov. 1869, p. 11. The 

 p. 327. Asa Gray, ' American Rev. G. Henslow also says ( ' Gar- 

 Journal of Science/ 2nd series, vol. dener's Chronicle, ' 1877, p. 271; 



