342 CONCLUDING REMARKS CHAP. VIII. 



The belief that the first step towards flowers being 

 rendered cleistogamic was due to the conditions to which 

 they were exposed, is supported by the fact of various 

 plants belonging to this class either not producing 

 their cleistogamic flowers under certain conditions, or, 

 on the other hand, producing them to the complete ex- 

 clusion of the perfect ones. Thus some species of Viola 

 do not bear cleistogamic flowers when growing on the 

 lowlands or in certain districts. Other plants when 

 cultivated have failed to produce perfect floAvers during 

 several successive years; and this is the case with Jun- 

 cus bufonius in its native land of Eussia. Cleistogamic 

 flowers are produced by some species late and by others 

 early in the season; and this agrees with the view that 

 the first step towards their development was due to cli- 

 mate; though the periods at which the two sorts of 

 flowers now appear must since have become much more 

 distinctly defined. We do not know whether too low 

 or too high a temperature or the amount of light acts 

 in a direct manner on the size of the corolla, or indi- 

 rectly, through the male organs being first affected. 

 However this may be, if a plant were prevented either 

 early or late in the season from fully expanding its 

 corolla, with some reduction in its size, but with no 

 loss of the power of self-fertilisation, then natural se- 

 lection might well complete the work and render it 

 strictly cleistogamic. The various organs would also, 

 it is probable, be modified by the peculiar conditions 

 to which they are subjected within a completely closed 

 flower; also by the principle of correlated growth, and 

 by the tendency in all reduced organs finally to disap- 



also 'Nature,' Oct. 19, 1876, p. ers are self-fertilised. On Lysima- 



543) "that when the autumn rhia, H. Muller, 'Nature,' Sept. 



draws on, and habitually in win- 1873, p. 433. Bouche, ' Sitzungrs- 



ter for such of our wild flowers as hnricht der (resell. Naturforsch. 



blossom at that season," the flow- Freunde,' Oct. 1874, p. 90. 



