184 



THE EVOLUTION THEORY 



visits of the humble-bees, as, for instance, Pedicularis asplenifol w ', 

 the fern-leaved louse-wort, a plant of the high Alps (Fig. 42). The 

 first thing that strikes us about this jDlant is the thickly tufted hair 

 covering on the calyx (&), which serves to keep off little wingless 

 insects from the flower ; then there is the strange left-sided twisting 

 of the individual flowers, whose under lip allows only a strong insect 

 like the humble-bee to gain access, towards the left, to the corolla- 

 tube (Ict), in the depths of which the nectar is concealed. While the 

 humble-bee is sucking up the nectar it becomes dusted over with 

 pollen from the anthers, which falls to dust at a touch, and when it 

 insinuates itself into a second flower its powdered back comes first 

 into contact with the stigma of the pistil (gr) which projects from 



Fig. 42. Alpine Louseworfc (Pedicularis asplenifolia). A, flower seen from 

 the left side, enlarged three times ; the arrows show the path by which the 

 humble-bee enters. B, the same flower, seen from the left, after removal of 

 the calyx, the lower lip and the left half of the upper lip. C, ovary (ov), 

 nectary (n), and base of style. D, tip of style, bearing the stigma. E, two 

 anthers turned towards one another, 0, upper lip. u, lower lip. gr, style. 

 st, anthers, kr, corolla-tube, k, calyx. 



the elongated bill-shaped under lip, dusting it over with the pollen 

 of the first visited flower. Butterflies and smaller bees cannot rob 

 this flower ; it is strictly a humble-bee's flower. 



There are not a few of such flowers adapted to a very restricted 

 circle of visitors, and in all of them we find contrivances which close 

 the entrance to all except what we may call the welcome insects ; 

 sometimes there are cushions of bristles which prevent little insects 

 from creeping up from below, or it is the oblique position of the 

 flower which prevents their getting in from the stem ; sometimes it is 

 the length and narrowness of the corolla-tube, or the deep and hidden 

 situation of the nectar, which only allows intelligent insects to find 

 the treasure. 



