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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 



FIG. 237. The pendent flower of Yucca, showing 

 position of stamens and the ribbed ovary. After 

 RILEY and TRELEASE. 



- 2 37) there are 



mens, and an ovary 

 ribbed lengthwise, with a fun- 

 nel-shaped stigmatic opening 

 in its top (Fig. 238). The 

 numerous small ovules occur 

 in rows beneath the furrows. 



FIG. 238 Longitudinal section of an 

 ovary of Yucca, showing the funnel- 

 shaped stigmatic opening (s), and the 

 rows of ovules attached to the wall 

 (o). After RILEY and TRELEASE. 



B 



FIG. 239. The position of Pronuba on 

 the stamen of Yucca when collecting 

 pollen (A) and when thrusting it 

 into the stigmatic funnel (B). Af- 

 ter RILEY and TRELEASE. 



