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Show 386 CROSS-FER'riLISA 1'ION. CIIAP. X. for verv many generations by self-fertilisation. This is the ~ase with the vari ties of Pisum sativum and of Lathyrus odoratus which are cultivated in England, and with Ophrys apifera and some other plants in a state of nature. Nevertheless, n1ost or all of these plants retain structures in an effici~nt state which cttnnot be of the least use excepting for crossfertilisation. V\T e have also seen reason to suspect that self-fertilisation is in some peculiar manner beneficial to certain plants; but if this be really the case, the benefit thus derived is far more than counterbalanced by a cross with a fresh stock or with a slightly different variety. Notwithstanding the several considerations just advanced, it seems to me highly improbable that plants bearing small and inconspicuous flowers have been or should continue to be subjected to selffertilisation for a long series of generations. I think so, not from the evil which manifest! y follows from self-fertilisation, in many cases even in the first generation, as with Viola tricolor, Sarothamnus, N emophila, Cyclamen, &c. ; nor from the probability of t~e evil increasing after several generations, for on this latter head I have not sufficient evidence, owing to the manner in which my experiments were conducte~. But if plants bearing small and inconspicuous flowers were not occasionally intercrossed, and did not profit by the process, all their flowers would probably have been rendered cleistogene, as they would thus have larg~ly benefited by having to produce only a small q~antity of safely-protected pollen. In coming to this c~nclusion, I have been guided by the frequency with which plants belonging to distinct orders ha;e be~; rendered cleistogene. But I can hear of no 1nstan of a species with all its flowers rendered permanently CHAP. X. INCONSPICUOUS FLOWERS. 3~7 cleistogene. Leersia makes the nearest approach to this state; but as already stated, it has been known to produce perfect flowers in one part of Germany. Some other plants of the cleistogene class, for instance Aspicarpa, ha:e failed to produce perfect flowers during several years In a hothouse ; but it does not follow that they would fail to do . so in their native country, any more than with Vandellia, which with me prodncefl only cleistogene flowers during certain years. Plants belonging to this class comn1only bear both kinds of flowers every season, and the perfect flowers of Viola canina yield :fine capsules, but only when visited by bees. We have also seen that the seedlings of Ononis minutissima, raised from the perfect flowers fertilised with pollen from another plant, \vere finer than those fi·om self-fertilised flowers; and this was likewise the case to a certain extent with Vandellia. As therefore no species which at one time bore small and inconspicuous flowers has had all its flowers rendered cleistogene, I must believe that plants now bearing small and inconspicuous flowers profit by their still remaining open, so as to be occasionally intercrosserl ?Y insects. It has been one of the greatest oversights In my work that I did not experimentise on such flowers, owing to the difficulty of fertilising them, and to my not having seen the importance of the subject.* ------ ----- * Some of the species of Solanum ~ould be good ones for such exper~ments, for they are said by H. Muller (' Befruchtuug,' p. 434:) to be unattractive to insects from not secreting uectar, not producing much. pollen, and not being very ~nsp1euous. Hence probably it Is th:lt, according to Verlot (' Production .de~ Varietes,' 1865, p. 72), the varieties of "Ies auberO'ines et les tomates" (species of Solu-num) do not intercross when they are cultivated near tog-ether; but it flhould be remembered that these are not endemic species. On the other band, the flowers of the common potato (S. tuberosum), though they do not secrete nectar (Kurr, ' Bedeutung der Nektnrien,' 1833, p. 40 ), yet cannot be ronsidered as inconspicuous. and they are somet.imcs visited by Diptera (Miiller) and, ns I have 2 c 2 |