442 HUTCHINSON'S POPULAR BOTANY 



rams it down effectually with a to-and-fro motion of her head. If. as is 

 commonly the case, another egg is deposited in the same pistil, and 

 after that a third, each act of oviposition is succeeded by a fresh act of 

 pollination ; but on each occasion a. different notch of the style is selected, 

 and thus a supply is ensured for the ovules in each carpel. How perfectly 

 the insect does its work may be gathered from the fact that artificial 

 attempts to cross-fertilize the Yuccas by means of brush-pollination are 

 rarely, if ever, successful. 



The larva hatches in about a week, and at first appears to live on the 

 degenerate and swollen ovules : but finally it enters one that is developing. 

 In this state it undergoes three different moults, its colour meanwhile 

 changing from a translucent white to a rosy hue ; and with the ripening 

 of the seeds, the larva attains its maturity. Just about the time the fruits 

 are hardening and ready to dehisce, and the seeds are already coloured, 



the maggot bores a passage through 

 the pod, makes its way to earth, 

 and, tunnelling several inches below 

 the surface, spins in its under- 

 ground fastness a tough silken 

 cocoon intermixed with the soil. 

 In this condition it remains during 

 the autumn, winter, and spring 

 months, and only assumes the 

 chrysalis state a few days before 

 the blooming of the Yuccas. The 

 FIG. 546.-BALSAM (Impatiens). chrysalis is armed with spines on 



The flowers are adapted to the visits of humble-bees. At first ii -i i i i i -i f 



the stamens mask the pistil and stand in the entrance to the the head and DaCK, by means OI 



wer - which it works its way to the sur- 



face, and in due time issues forth 



a perfect insect ; henceforth to live its little life above ground, and, in 

 conjunction with some chosen companion of the other sex, to carry on the 

 useful work which its parents have carried on before it. 



Of animals outside the great class Insecta which aid in bringing the 

 reproductive elements of plants together, the chief are snails and birds. 

 Delpino, indeed, divides the plants fertilized by animals into three groups : 

 I. Omithophilce, or bird-lovers ; II. Entomophilce, or insect-lovers ; and III. 

 Malacophilce, or snail-lovers. Groups I. and III. remain to be spoken of. 



The plants fertilized by the agency of snails are comparatively few 

 in number. The Marsh-calla or Snake-root (Calla pahwtris, figs. 544, 545) 

 may serve as an example; though its chief pollinators are carrion-loving 

 flies, which are attracted to the flowers by their offensive smell. Pond- 

 snails, however, crawl up the partially submerged stem to the spadix, 

 receive pollen from the anthers of the lower ring of flowers, and, continuing 

 their journey, pollinate the female flowers higher up. 



