Cleistogamous Flowers 423 



wealth of flowers, etc. corresponds entirely with Darwin's con- 

 clusions. It seems to me to follow clearly from his investigations 

 that there is no essential difference between cross-fertilisation and 

 hybridisation. The heterostyled plants are normally dependent on 

 a process corresponding to hybridisation. The view that specifically 

 distinct species could at best produce sterile hybrids was always 

 opposed by Darwin. But if the good results of crossing were ex- 

 clusively dependent on the fact that we are concerned with hybrids, 

 there must then be a demonstration of two distinct things. First, 

 that crossing with a fresh stock belonging to the same systematic 

 entity or to the same hybrid, but cultivated for a considerable time 

 under different conditions, shows no superiority over self-fertilisation, 

 and that in pure species crossing gives no better results than self- 

 pollination. If this were the case, we should be better able to 

 understand why in one plant crossing is advantageous while in 

 others, such as Darwin's Hero and the forms of Mimulus and 

 Nicotiana no advantage is gained ; these would then be pure species. 

 But such a proof has not been supplied ; the inference drawn from 

 cleistogamous and cleistopetalous plants is not supported by evi- 

 dence, and the experiments on geitonogamy and on the advantage 

 of cross-fertilisation in species which are usually self-fertilised are 

 opposed to this view. There are still but few researches on this 

 point ; Darwin found that in Ononis minutissima, which produces 

 cleistogamous as well as self-fertile chasmogamous flowers, the 

 crossed and self-fertilised capsules produced seed in the proportion 

 of 100 : 65 and that the average bore the proportion 100 : 86. The 

 facts mentioned on page 415 are also applicable to this case. 

 Further, it is certain that the self-sterility exhibited by many plants 

 has nothing to do with hybridisation. Between self-sterility and 

 reduced fertility as the result of self-fertilisation there is probably 

 no fundamental difference. 



It is certain that so difficult a problem as that of the significance 

 of sexual reproduction requires much more investigation. Darwin 

 was anything but dogmatic and always ready to alter an opinion 

 when it was not based on definite proof: he wrote, "But the veil 

 of secrecy is as yet far from lifted ; nor will it be, until we can say 

 why it is beneficial that the sexual elements should be differentiated 

 to a certain extent, and why, if the differentiation be carried still 

 further, injury follows." He has also shown us the way along 

 which to follow up this problem ; it is that of carefully planned 

 and exact experimental research. It may be that eventually many 

 things will be viewed in a different light, but Darwin's investi- 

 gations will always form the foundation of Floral Biology on which 

 the future may continue to build. 



