YUCCA MOTH AND YUCCA POLLINATION. 119 
(PI. 38, Fig. 1) and which would suggest another possible 
method of self-pollination, namely, by the stamens reaching 
an exceptional length. So far as any proof is concerned, 
this has never happened with any of the filamentose species, 
aud in any event must be of extremely rare occurrence. 
The mere accidental introduction of any of the pollen 
grains into the stigmatic liquor would in all probability 
serve to fertilize some of the ovules, though I doubt 
whether complete fructification could thus ensue. The 
stigmatic cavity varies very much in the amount of its 
- secretion, which is sometimes abundant and at other times, 
almost or quite absent, and both Professor Trelease and 
myself have noticed that it is more abundant on Yucca 
angustifolia in its native habitat than on eastern grown 
plants. 
PRONUBA THE ONLY INSECT POLLINIZER. 
In my earlier studies, while the mutually beneficial 
adaptations of Pronuba and Yucca were at once apparent, 
I was strongly inclined to believe that there must be, 
occasionally, accidental pollination of the flowers by other 
insects, more particularly because of the fact just mentioned 
that the fleshy-fruited species were reported to occasion- 
ally produce seed in regions in which, presumably, the 
Yueca moth did not exist. I became interested, therefore, 
in carefully studying the habits of all insects found asso- 
ciated with or found within the flowers of Yucca. I have 
particularly watched and observed the Pennsylvania Soldier- 
beetle (Chauliognathus pennsylvanicus, Pl. 38, Fig. 3), which 
is more commonly found within the flowers than any other, 
and which has a peculiar mouth structure which would lead 
one to suppose that it would have something to do in at- 
tempting to get at the stigmatic liquor. Without going 
into details, I may say that observations covering a 
period of nearly twenty years have only served to convince 
me of the incapacity in this respect of all other insects as- 
sociated with the plant. The Chauliognathus above men- 
tioned I have never found anywhere near the stigma. All 
