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. B 

 The insect visitor, on its way FlG> 328> Flower of Clerodendron 

 to the nectary, can hardly fail in two stages 



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

 ing Stamens of the flower in ture, while the pistil is still undeveloped 



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

 its earlier Stage, A, but it can- the stamens have withered, and the 



not deposit any pollen on the stigmas have se P arated > 1>ead y for the 

 J r reception of pollen. After Gray 



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 



stiff 



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 (stig, the 

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

 After Muller 



1% C. Thompsonioe. 



