THE FERTILISATION OF FLOWERS. 



333 



sophy which directs attention to the bearing of the facts of fertilisation 

 on the constitution and regulation of the world of life at large. 



FIG. 235. FLOWF.R OF SAGE. 



FIG. 236. FLOWER OF PEA DISSECTED. 



A very interesting mechanism for effecting cross-fertilisation is seen 



in the case of flowers which, like the peas, beans, and their leguminous 



neighbours, present a very characteristic form of blossom. These 



flowers possess ten stamens (Fig. 237), 



nine united to form a bundle, and one 



remaining single. The flower is peculiar 



in that it consists of one very large petal 



(Fig. 236, a), behind or above, two at 



the sides or " wings " (b b), and two united 



to form the boat-shape " keel " (c) below. 



When an insect alights on the side petals 



or "wings" (Fig. 237, al\ the keel (c) 



is thereby pressed downwards. The 



pollen of the stamens (st) and the tip of 



the pistil are made to project, so as 



respectively to dust the insect's breast 



with pollen, and to receive therefrom the 



foreign pollen gathered previously from 



another flower. Sprengel himself noticed 



that the union of the stamens favoured this 



conjoined action. When the weight of the 



insect's body is removed, the stamens and 



pistil resume their normal position. If, as Sir John Lubbock 



remarks, "the two ends of the wings (in a sweet-pea) be taken 



between the finger and thumb, and pressed down so as to imitate 



the effect produced by the pressure of an insect, the keel is 



FIG. 237. SECTION OF PEA. 



