404 



NA TURE 



[Sept. 17, 1874 



the access of the pollen to the female llower. Hence such plants 

 as a rule flower early in the spring. Again, in such flowers the 

 pollen is less adherent, so that it can easily be detached by the 

 wind,* which would manifestly be a disadvantage in the case of 

 most of those flowers which are fertilised by insects. 



Such flowers generally have the stigma more or less branched 

 or hairy, which evidently must tend to increase their chances of 

 catching the pollen. 



It is an almost invariable rule that wind-impregnated flowers 

 are inconspicuous, but the reverse does not hold good, and there 



are many flowers which, though habitually visited by insects, are 

 not brightly coloured. In some cases flowers make up by their 

 numbers for the want of individual conspicuousness. In others 

 the insects are attracted by scent ; indeed, as has already been 

 mentioned, the scent, as well as the colours of flowers, has no 

 doubt been greatly developed through natural selection, as an 

 attraction to insects.* But though bright colours and strong 

 odours are sufficient to attract the attention of insects, something 

 more is required. Flowers, however sweet smelling or beautiful, 

 ■would not be visited by insects unless they had some more sub- 



Fio. 5. 



stantial advantages to offer. These advantages are the pollen 

 and the honey ; though it ajipears that some flowers beguile 

 insects by holding out the expectation of honey which does not 

 really exist, just as some animals repel their enemies by resem- 

 iiling other species which are either dangerous or disagreeable. 



The pollen, of course, though very useful to insects, is also 

 essential to the flower itself ; but the scent and the honey, at 

 Ua%t ia their present development, are mainly useful to the plant 

 in securing the visits of insects, and the honey also sometimes in 

 causing the pollen to adhere to the proboscis of the insect. 



Among other obvious evidences that the beauty of flowers is 

 useful in consequence of its attracting insects, we may adduce 

 those cases in which the transference of the pollen is eflected in 

 dilTerent manners in nearly allied plants, sometimes even in 

 difl'erent S|iecies belonging to the same genus. 



Thus, Maha sylveslris and Mnlva rotundifolia, which grow in 

 the same localities, and therefore must come into competition, 

 are nevertheless nearly equally common. In both species the 

 young flowers contain a pyramidal group of stamens which 

 surround the as yet immature pistil, and produce a large quantity 



Fig. 7, 



of pollen, which cannot fail to dust any insect which may visit the 

 flower for the sake of its honey. In il/,(/,-w syhvstris (Fig. i), where 

 the branches of the stigma are so arranged that the plant cannot 

 fertilise iiself, the petali are large and conspicuous, so that the 

 plant is visited by numerous insects ; while in Malva lotunJiplia 

 (Fig- 2), the flowers of which are comparatively small and are 

 rarely visited by insects, the branches of the stigma are elongated 



* On the other hand, il is an advantage to wind-borne seedi to be some- 

 wnat tightly attached, because iliey arc then only removed by a high wind 

 which IS cipable of carrying iheni some distance. 



and twine themselves among the stamens, so that the flower can 

 hardly fail to fertilise itself. 



Another remarkable instance occurs in the genus Epilobium, 

 which is, moreover, specially interesting, because in E. aiigus- 

 lijiiliiim, as I have already mentioned, the curious fact was first 

 noticed that the pistil did not mature until the stamens had shed 

 their pollen. 7;'. angnstifoUum has conspicuous purplish-red 



* In confirmation of this it is stated that when insects are excluded, tho 

 blossoms last longer than is otherwise the case ; that when flowers are once 

 feitilised, the coroUa soon drops off", its function being performed. 



