. Plant studies; an elementary botany. Botany. 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 o
. Plant studies; an elementary botany. Botany. 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
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