INBREEDING, PARTHENOGENESIS, ASEXUAL REPRODUCTION 251 



since the pollen of one flower is carried by insects to the pistil of 

 another, which cannot be reached by its own pollen, either because it 

 ripens too early or too late, or because the stigma, notwithstanding 

 its proximity, is so placed as to be out of reach of the pollen from 

 the adjacent stamens. I showed, following the fundamental investi- 

 gations of Sprengel, Charles Darwin, Hermann Muller, and other 

 successors of Darwin, that the flowers may in a sense be regarded 

 as the resultants of the insect-visits, since all their accessory 

 adaptations — large coloured petals, fragrance, nectar, and even little 

 minutiae of colour and markings (honey-guides) — as well as their 

 detailed shape, as seen in ' landing stages,' corolla tubes, and so on, are 

 only intelligible when we refer their existence to natural selection. 

 We assume that each of these adaptations secured some advantage 

 for the species concerned, and that therefore their first beginnings as 

 slight germinal varieties were accepted, and were brought gradually 

 to their full expression by the united operation of germinal and 

 personal selection. This at least is how we should express ourselves 

 now that we have become acquainted with the factor of germinal 

 selection. The advantage secured by every such improvement in 

 a flower's means of attracting insects is obvious, as soon as it is 

 established that cross-fertilization is more advantageous for the species 

 than self-fertilization. 



We have discussed this already ; we saw that experiments insti- 

 tuted by Darwin proved that seedlings which had arisen through 

 cross-fertilization were superior to those arising through self-fertiliza- 

 tion, and that in many cases the mother-plant itself produced fewer 

 seeds when self-fertilized than when cross-fertilized. This discovery 

 afforded an explanation of the cross-fertilization of flowers by 

 insects which Sprengel had previously observed. We understand how 

 the flowers must have become so adapted through processes of selection 

 that they were unable to fertilize themselves, but attracted insects, 

 and, so to speak, compelled these to dust them with pollen from 

 another plant of the same species. We also understand how self- 

 fertilization remained possible for many flowers in the event of cross- 

 fertilization through insects not being effected, since after a certain 

 period of waiting, a curvature of the stamens or the pistil may take 

 place and lead to the stigma being dusted with the pollen of the same 

 flower. Obviously the development of fewer seeds is preferable to 

 complete sterility. It is a well-known fact that peculiar inconspicuous 

 and closed flowers, designed solely for self-fertilization, may occur 

 along with the open flowers, as in the case of the so-called cleisto- 

 gamous flowers of the violet ( Viola) and the little dead-nettle {Lamium 



