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. 
