FLOWERS ASH INSECTS. 



129 



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least two forms of flowers, which differ from one another 

 in the relative lengths of their stamens and styles. In the 

 accompanying illustrations of Houstonia (see Fig. 135) it 

 is to be noticed that in one flower the stamens are short 

 and included in the tube, and the style is long and pro- 

 jecting, with the four stigmas exposed well above the 

 tube. In the 

 other flower the 

 relative lengths 

 are exactly re- 

 versed, the 

 style being 

 short and in- 

 cluded in the 

 tube, and the 

 stamens long 

 and projecting. 

 It appears that 

 the pollen from 

 the short sta- 

 mens is most 

 effective upon 

 the stigmas of 

 the short styles, 

 and that the 

 pollen from the 

 long stamens is 

 most effective 

 upon the stig- 

 mas of the long styles : and as short stamens and long 

 styles, or long stamens and short styles, are associated in 

 the same flower, the pollen must be transferred to some 

 other flower to find its appropriate stigma. This means 

 that there is a difference between the pollen of the short 

 stamens and that of the long ones. 



In some cases there are three forms of flowers, as in one 



Fig. 135. Flowers of Houstonia, showing two forms of 

 flowers. In 1 there are short stamens and a long style ; 

 in 2 long stamens and short style. An insect visiting 1 

 will receive a band of pollea about the front part of its 

 body ; npon visiting 2 this band will rub against the 

 stigmas, and a fresh pollen band will be received npon 

 the hinder part of the body, which, npon visiting another 

 flower like Xo. 1, will brush against the stigmas. — 

 After Gray. 



