369 
state about a week before the Yuccas bloom again, and finally issues 
as a moth to continue the annual cycle of its career. The chrysalis 
(Fig. 67) has a capitate spine and a series of dorsal spines, some of 
which are spatulate and admirably fitted for helping it to work through 
the ground. 
The effect of the puncture of the female moth on the fruit is at 
onee noticeable by a darker green discoloration externally. In time 
this becomes a depression, causing a constriction of the pod, and the 
irregularities of the pod (Fig. 68, b, ¢), which have been supposed to 
be characteristic of the genus Yucca, are really due to these punctures, 
which ordinarily occur just below the middle. The absolute need of 
WON 
a ee ae 
<7 eN. 
Fic. 68.—Mature pods of Yucca angustifolia: a, artificially pollinized and protected from Pronuba; 
b, normal pod, showing constrictions resulting fron. Pronuba puncture and exit holes of larva; c, one 
of the lobes cut open, showing larva within. 
Pronuba in the pollination of our dehiscent Yuceas I have proved over 
and over again in many ways. The plant never produces seed where 
Pronuba does not exist; it never produces seed when she is excluded 
artificially, and experiments which J have made with artificial or brush 
pollination all show that it is much more difficult to insure complete 
fructification than would at first appear, and that the act of pollination 
is rarely performed with a brush or by using the flower’s own filaments 
as successfully as it is done by Pronuba. It is Pronuba yuccasella 
which pollinizes all our Yuceas east of the Rocky Mountains, so far as 
known, and the species is remarkably uniform in character, its appear- 
ance being coetaneous with the flowering of Yucca filamentosa. Onthe 
western plains its appearance has become adapted to the flowering of 
Yucca angustifolia, but in the east, where these two species of Yucca 
are frequently grown side by side, Y. angustifolia flowers two or three 
weeks earlier than Y. filamentosa, and generally too early to receive the 
visits of Pronuba, so that it produces seed only on very rare occasions. 
