244 A TEXT-BOOK OF BOTANY 
146. Yucca and Pronuba.—This is a remarkable case of 
self-pollination by means of an insect. Yucca is a plant 
of the southwest- 
ern arid regions 
of North America, 
and Pronuba is a 
moth; and the two 
are very dependent 
upon each other. 
The bell - shaped 
flowers of Yucca 
hang in great ter- 
minal clusters. In 
each pendent flower 
Fic. 237.—The pendent flower of Yucca, showing (Fig. 237) there are 
position of stamens and the ribbed ovary.—After sjx hanging sta- 
RiLey and TRELEASE. 
mens, and an ovary 
es ane ribbed lengthwise, with a fun- 
as nel-shaped stigmatic opening 
in its top (Fig. 238). The 
numerous small ovules occur 
in rows beneath the furrows. 
RR, 
s 
Fic. 238 —Longitudinal section of an Fia. 239.—The position of Pronuba on 
ovary of Yucca, showing the funnel- the stamen of Yucca when collecting 
shaped stigmatic opening (s), and the pollen (A) and when thrusting it 
rows of ovules attached to the wall into the stigmatic funnel (B).—Af- 
(o).—After R1nEy and TRELEASE. ter Riney and TREUEASE. 
