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 larve 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 larve 
hatch and feed upon the growing seeds, some of which, 
however, are left uninjured, and ripen after the rest 
have been eaten by the larve. 
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 (Dionza), 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 Diona, 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 
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