78 BOTANICAL GAZETTE [JULY 
improbable, judging by the cases of other insects, but the factor 
of elimination of some of the eggs and larvae remains, and the 
advantage, from whatever cause, is to the plant. 
In conclusion it is to be noted that Yucca is a successful plant in 
regions where the climatic conditions are requisite and Pronuba 
is found. The peculiar method of pollination by a single insect 
species, which is maintained at the expense of the plant, must then 
also be considered successful. The. averages show that it is. An 
average pod produces 300 seeds, over 100 of which are perfect, at a 
loss of 58 seeds, that is 21 per cent of the total production. 
UnIversity oF CoLorapo 
BouLpEr, Cotorapo 

