170 GENEKAL BOTANY 



conjunction with the maturing of the stigma, and the anthers are 

 so placed that the pollen is dusted onto the hairs of the stigmatic 

 surface when the anthers dehisce. Self-pollination is thus in- 

 sured, even though insect visitors are artificially excluded. On 

 the other hand, these flowers are admirably adapted, in many 

 respects, to close-pollination or cross-pollination. The conspicuous 

 standard serves as a flag apparatus, and the nectar is so located 

 at the base of the flower that visiting insects are tempted to 

 probe into the flower for it. The wing petals serve to support 

 the visiting insect ; and since they are attached to the keel, this 

 structure is certain to be depressed by the weight of the insect's 

 body. The depression of the keel petals results in the exposure 

 of the anthers and the hairs on the style, which snap up against 

 the insect's body through the opening between the keel petals. 

 The hairy abdomen of the visiting insect is thus covered with 

 pollen, which may be borne to other flowers on the same plant, 

 thus effecting close-pollination, or to flowers on different plants, 

 effecting cross-pollination. The structure of the pea flower, 

 like that of species which are wholly .unable to secure self- 

 pollination, thus manifests remarkable adaptations for securing 

 close-pollination or cross-pollination. In the two examples which 

 follow, selected from the pea family, either close-pollination or 

 cross-pollination is assured, and self-pollination is prevented by 

 the structure of the flower and by the relative positions of the 

 anthers, the style, and the stigma. 



The locust and red clover. The flower of the common locust 

 may be used, in contrast with that of the pea, as a concrete 

 example of an elaborate adaptive mechanism in a flower of the 

 pea family, designed to insure either close-pollination or cross- 

 pollination. The general arrangement and shape of the floral 

 parts in the locust flower are so similar to those of the pea 

 blossom just described that no additional description is necessary 

 (Fig. 90, <?). The special devices for insuring close-pollination 

 or cross-pollination are concerned, as indicated above, with the 

 structure of the perianth, the peculiarities of the pistil, and the 

 relations of the anthers to the style and the stigma. The style, as 

 in the pea blossom, bends so as to make a right angle with the 



