130 



PLANT STUDIES 



of the common loosestrifes. Each flower has stamens of 

 two lengths, which, with the style, makes possible three 

 combinations. One flower has short stamens, middle-length 

 stamens, and long style ; another has short stamens, middle- 

 length style, and long stamens ; the third has short style, 

 middle-length stamens, and long stamens. In these cases 

 also the stigmas arc intended to receive pollen from stamens 



Fio. 136. Yucca and F/onitha. In the louer figure to the riglit :in opened flower 

 shows the pendent ovary with the stignia region at its apex. Tlie npper ligure to 

 the right shows the position of Pronuba when collecting pollen. The fignre to the 

 left represents a cluster of capsules of Yucca, which shows the perforations made 

 by the larvae of Pronuba in escajjing.— After Kiley and Tkelease. 



of their own length, and a transfer of pollen from flower to 

 flower is nocfssary. 



90. Self-pollination. — In considering these tliree general 

 metliods of preventing self-pollination, it must not lie sup- 

 posed tliat self-pollination is never provided for. It is pro- 

 vided for more extensively than was once supposed. It is 

 found tluit iiKtny ])lants, such ;is violets, in aildition to tlie 

 usual sliowy, iusect-polliiiiited flowers, produce flowers that 

 are not at all showy, in fa.ct do not open, and are often not 

 prominently iilaeed. 'Y\n\ fact that these flowers are often 

 closed has suggested for tliem the name deistogamous 



