POLLINATION AND FECUNDATION. 



51 



that insects entering the throat of the corolla, for the purpose 

 of getting nectar, would necessarily brush the pollen on to 



stigma 



1^ ~ 



Fig. 73. 



Fig. 74. 



Fig. 75. 



Fig. 76. 



their bodies from the end of the protracted stigma (Fig. 74). 

 The stigmatic surface finally becomes exposed (Figs. 75, 76). 

 It is evident that self-pollination is impossible; and cross- 

 pollination by the insects, which transport the pollen from 

 flowers in the first stage of maturity to those in the second 

 stage, must take place. 



9. Dimorphism (Gr. di, two ; morphe, form) denotes the ex- 

 istence of two kinds or forms of hermaphrodite flowers of the 

 same species. It is often an adaptation for intercrossing. An 

 example is furnished by the Houstonia. One set of flowers 

 has long stamens and a short pistil (Fig. 77), and the other set 

 has short stamens and a long pistil (Fig. 78). A bee visiting 

 the different flowers would brush some part of its body against 



Fig. 77. 



Fig. 78. 



Fig. 79. 



the anthers of the long stamens, and another part against the 

 anthers of the short stamens ; and these same parts (which, 

 of course, would have pollen adhering to them) coming in 



