252 THE EVOLUTION THEORY 



amplexicaule), and the phyletic origin of these becomes intelligible 

 as soon as it is established that cross-fertilization is more advantageous 

 than self-fertilization. 



Now, however, it seems as if the fundamental proposition of this 

 theory of flowers will have to be rejected. Not only do the cleisto- 

 gamous flowers just mentioned exhibit a great fertility, not at all less 

 than that of the open flowers of the same species which are adapted 

 for cross-fertilization, but there is a small number of plants which 

 produce seeds by self-fertilization alone. Thus in Mynnecodia cross- 

 fertilization is absolutely prevented by the fact that the flowers never 

 open, and according to Charles Darwin O'phrys apifera also repro- 

 duces by self-fertilization alone, and is nevertheless a thoroughly 

 vigorous plant. There are several other cases of this sort, and par- 

 ticularly among the orchids, though the whole of the structure of 

 their flowers is specially adapted for pollination by insects. Many 

 of them are only rarely visited by insects, some not at all, we know 

 not why, but it is readily intelligible that in such cases they should 

 have adapted themselves to self-fertilization wherever that was pos- 

 sible. For this no great variation was necessary ; it was enough that 

 the pollinia, which formerly only became detached from their attach- 

 ment at a touch or a push from an insect, should free themselves 

 spontaneously. And this, according to Darwin, is what happens, for 

 instance, in Ophrys scolojxix, which at Cannes is frequently self- 

 fertilizing. For the development of seed, however, it is not enough 

 that the pollen should reach the stigma ; the pollen -grain has to send 

 out its tube and penetrate into the ovary, and in many orchids this 

 does not happen ; they are infertile with their own pollen. Various 

 other plants are also non-fertile with their own pollen, for instance the 

 common corydalis, Corydalis cava, or the meadow cuckoo-flower, 

 Cardainine pratensis (Hildebrand). 



How are we to reconcile these apparently absolutely contra- 

 dictory facts ? On the one hand, the innumerable devices for securing 

 crossing lead us to conclude that it is necessary, or at least advan- 

 tageous, and on the other we find a small number of plants which 

 reproduce continually by self-fertilization and yet remain strong and 

 vigorous. And again there are many plants which yield seed when 

 fertilized with their own pollen, and others which remain absolutely 

 sterile in the same circumstances, yielding no seed or very little, and 

 there is indeed one on ^vhich its own pollen has the effect of a poison, 

 for if it reaches the stigma the flower dies. If there is anytliing 

 injurious in self-fertilization (Darwin), we can understand that it will 

 be avoided, but how can it be continued so long in many cases, and 



