YUCCA MOTH AND YUCCA POLLINATION. 115 
depression, and the irregularities of the pods (PI. 34, Fig. 
5, . c.) which have been considered characteristic of the 
fruit of the genus are chiefly due to these punctures, which, 
ordinarily occurring just below the middle of the pod, 
produce a more or less marked constriction there. This I 
have often proved by artificially pollinizing the flowers 
and protecting them from Pronuba, when the pods will 
develop in a regular, parallel-sided manner (PI. 34, Fig. 
5,a.) Internally the effect of the puncture is no less 
marked. A few of the ovules in the region of the punc- 
ture are at once affected, as already described, while the 
development of a yet larger number is more or less arrested, 
this being the case even when not touched by the ovipositor 
or the egg, or even where the egg fails to hatch. Did the 
ovules develop immediately around the egg it is probable 
that they would crush it. At Pl. 35, Fig. 2 d is showna 
section of a carpel 7 days old with egg, and of another, e, 
with the larva just hatched. 
EFFECT OF FERTILIZATION ON THE STALK. 
It is an interesting fact that, however pollinized, whether 
by Pronuba or artificially, each Yucca panicle will mature 
but a certain number of pods, so that a number of those 
which are fructified drop after a few days’ development, 
while some wither even after they have reached nearly full 
development. This gives an element of uncertainty to 
experiments and makes it necessary to be very careful. 
It is interesting also to note how the mere fact of fruc- 
tification influences the main stalk, at least in Y. filamen- 
tosa, for where a panicle is protected with gauze, so as te 
prevent the access of Pronuba, and cause the dropping of 
all the flowers, the stalk soon thereafter withers and dies. 
DATES OF THE FLOWERING OF THE YUCCAS AND APPEARANCE 
OF THE MOTH. 
There is some irregularity in the flowering of our Yuccas, 
even of those of the same species. The typical form of 
