Lastly, there is a large number of plants, including a great proportion of those with unsymmetrical blossoms, of which the flowers have been shown to be specially adapted by various mechanical contrivances for insect agency. Nothing, as is well known, is more marvellous than the variety and subtlety of the arrangements for the purpose which exist in orchidaceous plants, as explained by the patience and genius of Mr. Darwin. In view of these facts it would be impossible to deny that conspicuousness is one of the agencies in force for the fertilization of flowers; that, to use the recent language of Mr. Darwin, "flowers are not only delightful for their beauty and fragrance, but display most wonderful adaptations for various purposes."[7] So far we have considered the evidence which is affirmative, and in favour of the explanation of the existence of beauty in flowers; we have found clearly that beauty, or rather conspicuousness, is in many cases useful to the plant. But beauty is by no means the only agency in this necessary process. On the contrary, the agencies actually in operation are very numerous. As Mr. Darwin points out in the passage I have cited, and still more at large in his work "On the Different Forms of Flowers," a large proportion of existing plants are fertilized by the action of the wind; and again, many plants bear two kinds of flowers, the one conspicuous and attractive to insects, the other inconspicuous and which never open to admit the activity either of insects or of the wind. Moreover, there are various other agencies called into play. Some plants, such as the _Hypericum perforatum_, one of the commonest of the St. John's Worts, and probably the bindweed, are, it seems, fertilized by the withering of the corolla, which naturally brings the stamens into contact with the style, and so transfers the pollen grains from the one to the other.[8] Other plants, again, such as the common centaury (_Erythræa centaurium_) and the _Chlora perfoliata_, are fertilized by the closing of the corolla over the anthers and stigma, not in the death but in the sleep of the plant.[9] In the brilliant autumnal _Colchicum_, and in the _Sternbergia_, again, according to Dr. Kerner, Nature has recourse to a more complex machinery: the corolla first closes over the anthers, which are at a lower level than the stigma, and takes off some of the pollen; a growth of the corolla carries the pollen dust to the level of the stigma, and a second closing of the corolla transfers the pollen to the stigmatic surface. The pollen has been made to ascend to its proper place by an arrangement which reminds one of the man-engine of a Cornish mine.[10] A similar arrangement is described as occurring in the bright-flowered _Pedicularis_.[11]