ECOLOGY OF FLOWERS ; POLLIXATION 



175 



Many flowers which appear to be designed to secure 

 self-pollination are almost or quite incapable of it. Fre- 

 quently the pollen from another plant of the same species 

 prevails over that which the flower may shed on its own 

 pistil, so that when both kinds are placed on the stigma 

 together it is the foreign pollen which fertilizes. 



209. Dichogamy ; Movements of Stamens. — If the sta- 

 mens mature at a different time from the pistils, self- 

 pollination is as effectually 

 prevented as though the 

 plant were dioecious. This 

 unequal maturing, or di- 

 chogamy, occurs in many 

 kinds of flowers. In some, -i 

 the fiffwort and the com- 



mon plantain for example, 

 the pistil develops before 

 the stamens, but usually 

 the reverse is the case. The 

 Clerodendron,^ a tropical 

 African flower (Fig. 131), 

 illustrates in a most strik- 

 ing way the development 

 of stamens before the pistil. 

 Besides the slow move- 

 ments ^^-hich the stamens 

 and pistil make in such 

 cases as that of the Clerodendron, the parts of the flower 

 often, as in the barberry and Kahnia, admit of extensive 

 and rather quick movements to assist the insect visitor to 

 become dusted or smeared with pollen. 



1 C. Thompsoniss. 



rio-n-er of Clerodendron in 

 Two Stages. 



In A (earlier stage) tlie stamens are ma- 

 ture, Tvliile the pistil is still undevel- 

 oped and bent to one side. In B (later 

 stage) the stamens have "withered and 

 the stigmas have separated, ready for 

 the reception of pollen. 



