THE FLOWER 243 
the wind, it is clearly to the advantage of a plant to attract 
such visitors, even at the expense of a little honey, or of a 
liberal toll out of the pollen they distribute. 
2478. Special partnerships. — Some plants have adapted 
themselves to the visits of one particular kind of insect so 
completely that they would die out if that 
species were to become extinct. The well- 
known alliance between red clover and the 
bumblebee was brought to light when the 
plant was first introduced into Australia. 
It grew luxuriantly and blossomed pro- 
fusely, but would never set seed till the 
bumblebee was introduced to 
keep it company. 
- oe on A remarkable partnership of 
the Pronuba yu- this kind exists between the 
ale, pronuba, or yucca moth, and 
the flowering yuccas, of which the bear’s grass 
and Spanish bayonet are familiar examples. 
The pods of these plants are never perfect, but \ oa! 
all show a constriction at or near the middle, Bey Se 
such as is some- Ir 
times seen in on 
the sides of 5 20h. vom: 
wormy plums nating pistil of 
and pear" 
This is caused by the larvee 
of the moth, which feed upon 
: the unripe seeds. A glance 
Fic. 354.— Moth resting on yucca under the nodding perianth 
ae of a yucca blossom (Fig. 354) 
will show that the short stamens are curved back from the 
pistil in such a manner that, under ordinary circumstances, 
the pollen cannot reach the stigma except by the rarest 
accident. But the yucca moth, as soon as she has deposited 
her eggs in the seed vessel, takes care to provide a crop of 
