:hap. VI] 



ANIMALS 



133 



terile, depends on Pronuba yuccasella for its fertilization (Fig. 69). As 

 he insect is just as dependent on the Yucca for its multiplication, it is 

 lifficult to say which of the two organisms determines the geographical 

 listribution of the other. 



The process of pollination in the Yucca is extremely peculiar. The moth lays 

 ts eggs in the ovar}^ in which the larvae have to develop at the expense ot 

 he young seeds. In order to render the development of the seeds possible, the 

 10th effects pollination b}' introducing pollen into the stigma. Since many seeds 



/.^ 



Fig. 6g. Yucca filamentosa flower and (after Kerner) the moth (Pronuba yuccasella). 



Natural size. 



5 produced and only a few larvae, both organisms profit equally. Other species 

 Yucca are pollinated bj' other species of Pronuba ; for example. Yucca Whipplei 

 California by Pronuba maculata, Yucca brevifolia in the Mohave desert by 

 onuba synthetica. 



The dependence of certain plants on their pollinators is also strikingly 

 :hibited in red clover. This plant is pollinated exclusively by humble- 

 es. In New Zealand there are no humble-bees, and red clover therefore 

 mains sterile. In recent times, therefore, humble-bees have been im- 

 rted to New Zealand in order that pollination and consequent seed- 

 'mation may take place'. 

 Further observations, especially in any countries that have remained 



^ Belt, II. 



