PREVENTION OF SELF POLLINATION 



429 



dioecious. This unequal ma- 

 turing, or dichogamy , occurs 

 in many kinds of flowers. In 

 some, the figwort and the com- 

 mon plantain for example, the 

 pistil develops before the sta- 

 mens, but usually the reverse 

 is the case. The Clerodendron} 

 a tropical African flower (Fig. 

 328), illustrates in a most 

 striking way the development 

 of stamens before the pistil. 

 The insect visitor, on its wav 



i/ 



to the nectary, can hardly fail 



V ' V 



to brush against the protrud- i n A (earlier stage) the stamens are ma- 



ing stamens of the flower in 

 its earlier stage, A, but it can- 

 not deposit any pollen on the 

 stigmas, which are imma- 

 ture, shut together, and tucked aside out of reach. On flying 

 to a flower in the later stage the pollen just acquired will be 



FIG. 328. Flower of Clerodendron 



in two stages 



ture, while the pistil is still undeveloped 

 and bent to one side. In B (later stage) 

 the stamens have withered, and the 

 stigmas have separated, ready for the 

 reception of pollen. After Gray 



A B C D 



FIG. 329. Provisions for cross pollination in the high mallow 



A, essential organs as found in the bud; B, same in the staminate stage, the 

 anthers discharging pollen, pistils immature; C, intermediate stage (stiff, the 

 united stigmas) ; I), pistillate stage, the stigmas separated, stamens withered. 

 - After Miiller 



1 C. Thompsonice. 



