FLOWEBS AND INSECTS 



125 



in solving these problems. They often fail, but succeed 

 often enough to niiike the effort worth while. 



89. Preventing self-pollination. — It is evident that this 

 danger arises only in those flowers in which the stamens 

 and carpels are associ 



ated, but their separa- ^. ' ^ 2 



tion in different flowers 

 may l)e considered as 

 one method of prevent- 

 ing self-pollination. In 

 order to understand the 

 various arrangements to 

 bo considered, it is nec- 

 essary to explain that 

 the carpel does not re- 

 ceive the 2>ollen indif- 

 ferently over its whole 

 surface. There is one 

 definite region organ- 

 ized, known as the 

 stigma, upon which the 

 pollen must be deposited 

 if it is to do its work. 

 Usually this is at the 

 most projecting point 

 of the carpel, very often 

 at the end of a stalk- 

 like prolongation from 

 the ovary (the bulbous 

 part of the carpel), 

 known as the style ; 

 sometimes it may run down one side of the style. "When 

 the stigma is ready to receive pollen it has upon it a 

 sweetish, sticky fluid, which holds and feeds tlie pollen. 

 In this condition the stigma is said to be mature ; and the 

 pollen is mature when it is shedding, that is, ready to fall 



Fig. 131. Parts of the flowx-r of rose acacia 

 (Roliiniahu'pU/a). In 1 the keel is shown pro- 

 jecting from tlie hairy calyx, the other more 

 ehowy parts of the corolla having been re- 

 moved. Within the Iceel are the stamens 

 and the carpel, as seen in 3. Thel;eel forms 

 the natural landing place of a visiting; bee, 

 \vhose weight depresses the keel and causes 

 the tip of the style to protrude, as shown in 

 2. This style tip bears pollen u[)on it, 

 caught among tlie hairs, seen in 3, and as it 

 strilies the body of tlie bee some poUeu is 

 bruslied off. If the bee lias previously visited 

 another flower and received some pollen, it 

 will be seen tliat the stigma, at the very tip 

 of the style, strilving the body first, will very 

 probably receive some of it. Tlie nectar pit 

 is shown in 3, at the base of the up]jermost 

 stamen. — After Ghay. 



