186 THE EVOLUTION THEORY 



an enlargement at the base, in which both pistil and stamens are con- 

 tained. In the birthwort (Fig. 43) the narrow entrance-tube is thickly 

 beset with stiff hairs {A, b), whose points are all directed towards 

 the base. Little flies can creep down quite comfortably into the basal 

 expansion, but once there they are kept imprisoned until the flower, 

 in consequence of the pollination of the stigma, begins to wither, the first 

 parts to go being these very bristles {B, b'), whose points, like a fish- 

 weir, prevented the flies from creeping out. Other ' fly-flowers,' as for 

 instance the Alpine butterwort {Pinguicula alpina) (Fig. 44), securely 

 imprison the plump fly as soon as it has succeeded in forcing itself in 

 far enough to reach, with its short proboscis, the nectar contained in 

 the spur {sp) of the corolla. The backward-directed bristles hold it 

 fast for some time, and it is only by hard pressing with the back 

 against the anthers (si) lying above it, and against the stigma {n), 

 that it ultimately succeeds in getting free, but it never does so without 

 having either loaded itself with pollen, or rubbed off on the stigma 

 the pollen it brought with it from another similar flower. The Alpine 

 butterwort is protogynous, that is to say, the pistil ripens first, the 

 pollen later, so that the possibility of self-fertilization is altogether 

 excluded. 



It would be impossible to give even an approximate idea of the 

 diversity of the contrivances for securing fertilization in flowers 

 without spending many hours over them, for they are different in 

 almost every flower, often widely so, and even in species of the same 

 genus they are by no means always alike ; for not infrequently one 

 species is adapted to one circle of visitors, and its near relative to 

 another. Thus the flower of the common Daphne {Daphne mezereum) 

 (Fig. 45, A and C) is adapted to the visits of butterflies, bees, and hover- 

 flies, while its nearest relative (Daj^hne striata) (Fig. 45, B and -D) has 

 a somewhat narrower and longer corolla-tube, so that only butterflies 

 can feast upon it. This example shows that there are exclusively 

 ' butterfly flowers,' but specialization goes further, for there are flowers 

 adapted to diurnal and others to nocturnal Lepidoptera. The former 

 have usually bright, often red colours, and a pleasant aromatic 

 fragrance, and in all of them the nectar lies at the bottom of a very 

 narrow corolla-tube. To this class belong, for instance, the species of 

 pink, many orchids, such as Orchis ustulata, and Nigritella angusti- 

 folia of the Alps, which smells strongly of vanilla ; also the beautiful 

 campion {Lychnis diurna) and the Alpine primrose {Primula farinosa). 

 The flowers adapted to nocturnal Lepidoptera are characterized by 

 pale, often white colour, and a strong and pleasant smell, which only 

 begins to stream out after sunset, and indeed many of these flowers 



