ANIMALS AND PLANTS 257 



most interesting topic here. The works of Darwin, 

 Miiller, and others may be consulted by those who 

 desire to become further acquainted with the really 

 astonishing contrivances found among the orchids. 



In most instances, flowers are visited by insects either 

 for nectar or for pollen, but there are some exceptions to 

 this. One of the most remarkable cases is that of vari- 

 ous species of Yucca, which are most abundant in the 

 arid regions of southwestern America. In the species 

 which have been investigated, the agent in pollination 

 is a small moth of the genus Pronuba, whose larvae feed 

 upon the young seeds. The moth deposits its eggs in 

 the young ovary of the flower, and then deliberately 

 crowds a mass of pollen into the canal of the stigma, 

 thus insuring the fertilization of the ovules. The larvae 

 hatch and feed upon the growing seeds, some of which, 

 however, are left uninjured, and ripen after the rest 

 have been eaten by the larvae. 



A very remarkable group of plants are those known 

 as " carnivorous " or " insectivorous " plants, which in- 

 stead of being eaten by animals, themselves capture 

 and devour insects and other small animals. In some 

 instances, like the common sundew (Drosera) (Fig. 58, 

 C, D) and Venus's flytrap (Dionsea), the insects are cap- 

 tured alive, and actually digested. In these plants the 

 leaves are sensitive, and an insect alighting upon a leaf 

 is either held fast by means of a sticky secretion, which 

 increases in amount as the leaf is stimulated by the 

 movements of the insect, and then slowly folds up about 

 it ; or, in Dionaea, the blade of the leaf is arranged much 

 like the jaws of a spring-trap, and closes up quickly 

 when the insect touches certain sensitive hairs upon 



