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Show 384 CROSS-FERTILISATION. CHAP. X. for only eight or nine out of the 125 species in the two lists coine under this head, and all of these were proved to be highly fertil~ when insects were excluded. The singularly inconspicuous flowers of the Fly Ophrys (0. muscifera), as I h~v~ elsewhere ~hown, are rarely visited by insects; and It Is a strange Instance of iinperfection, in contradiction _to the above rule, that these flowers are not self-fertile, so that a large proportion of them do not pr~cluc seeds. !he co~verse of the rule that plants beanng small and InconspiCuous flowers are self-fertile, namely, that plants with large and conspicuous flowers are self-sterile, is far from true, as may be seen in our second list of spontaneously self-fertile species ; for this list includes such species as lpo1ncea pu?"purea, Adonis mstivaUs, Verbascum th.apsus,. Pisurm sativum, Lathyrus odoratus, some spemes of Papaver and of Nymphroa, and others. The rarity of the visits of insects to small flowers, does not depend altogether on their inconspicuous~ess, but likewise on the absence of some sufficient attractiOn; . for the fio\vcrs of Trifolium a.rvense are extremely small, yet are incessantly visited by hive and humblebees as are the sinall and dingy flowers of the aspa~agus. The flowers of Linaria cymbalaria . are small and not very conspicuous, yet at the proper time they are freely visited by hive-bees. I may add th~t, according to Mr. Bennett,* there is another and qmte distinct class of plants which cannot be much frequented by insects, as they flower either exclusively or often during the winter, and these seem adapted for selffertilisation, as they shed their pollen before the flowers expand. . rfhat Inany flowers have been rendered conspiCUOUS * 'Nature,' 1869, p. 11. CHAP. X. INCONSPICUOUS FLOWERS. 385 for the sake of guidi~g insects to them is highl probable or almost certain ; but it may be asked, hav~ other flowers been rendered inconspicuous so that they ~aY. not be frequently :is~t~d, or have they merely :retained a former an~ pr:mitive condition ? If a plant were much reduced In size, so probably would be the flowers through correlated growth, and this may possibly account for some cases ; but the size and colour of the corolla are both extremely variable characters, and it can hardly be doubted that if large and brightly-coloured flowers were advantageous to any · h speme~ t .es~ could be acquired through natural selection within a .moderate lapse of time, as indeed we see with most alpine plants. Papilionaceous flowers are manifest!~ construc~ed in relation to the visits of insects, and It seems Improbable, from the usual character of the p-r~up: that the progenitors of the genera Vicia and rnfohum produced such minute and unattractive flowers as those of V. hirsuta and T. procumbens. We are thus_ led to infer that some plants either have not had theu flowers increased in size, or have actually ha~ them reduced and purposely rendered incon~ piCuous, so that they are now but little visited by Insects: In either case they must also have acquired or re~ained a high degree of self-fertility. . If It beca~e from any cause advantageous to a speCies to_ ha:e Its ~apacity for self-fertilisation increased, ther~ Is httle difficulty in believing that this could ~eadily be effected; for three cases of plants varyin a In such a manner as to be more fertile with their 0\1'~ pollen than they originally were, occurred in the course of £ · I my ew expenments, namely, with Mimulus dp omcea ' a n d N' t· ' I co I ana. Nor is there any reason to f: oubt that many kinds of plants are capable under avourabl · e Circumstances of propagating themselves 2 a |