340 CONCLUDING REMARKS Chap. VIII. 



Voandzeia; and in this case we should remember that 

 cultivation often affects injuriously the reproductive or- 

 gans. Although the perfect flowers of Leersia some- 

 times yield seeds, yet this occurs so rarely, as far as 

 hitherto observed, that it practically forms a second ex- 

 ception to the rule. 



As cleistogamic flowers are invariably fertilised, and 

 as they are produced in large numbers, they yield al- 

 together a much larger supply of seeds than do the per- 

 fect flowers on the same plant. But the latter flowers 

 will occasionally be cross-fertilised, and their offspring 

 will thus be invigorated, as we may infer from a wide- 

 spread analogy. But of such invigoration I have only 

 a small amount of direct evidence: two crossed seed- 

 lings of Ononis minutissima were put into competition 

 with two seedlings raised from cleistogamic flowers; 

 they were at first all of equal height; the crossed were 

 then slightly beaten; but on the following year they 

 showed the usual superiority of their class, and were to 

 the self -fertilised plants of cleistogamic origin as 100 

 to 88 in mean height. With Vandellia twenty crossed 

 plants exceeded in height twenty plants raised from 

 cleistogamic seeds only by a little, namely, in the ratio 

 of 100 to 94. 



It is a natural inquiry how so many plants belong- 

 ing to various very distinct families first came to have 

 the development of their flowers arrested, so as ulti- 

 mately to become cleistogamic. That a passage from 

 the one state to the other is far from difficult is shown 

 by the many recorded cases of gradations between the 

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

 tum, Campanula, &e. 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. 



