APPENDIX A 



D-j 



transmitted by their interlocking surfaces to the keel, which is thus depressed, 

 and yields. The stiff stamens and carpel do not yield, and so first the stigma, 

 and then the anthers with their pollen project through a pore which is left 

 open at the tip of the keel. When the weight of the bee is removed the keel 

 rises, and the stamens and stigma are again enveloped, and are ready for a 

 fresh insect visit. The effect of such visits will he, first, to rub the stigma, and 

 make it receptive, while as it emerges first from the keel it receives any pollen 

 brought from other flowers by the bee ; second, to deposit a fresh supply of 

 pollen on the insect. A cross-pollination is thus a virtual certainty. 



Fig. 431. 



Flower^'of Lotus cornicidatus, L.'JI. flower complete. II. with vexillum removed. 



III. with alae and part of carina removed. IV. carina slit longitudinally. V. one of 



the alae. VI. stamens of different length. VII. carpel in section. VIII. floral 



diagram. s=sepals; u=vexillum; ^1 =alae; c=carina; s = stamens ; st -stigma. 



(31) The flower of the Garden Pea {Pisum sativum), may be taken as an 

 alternative type, the construction being essentially the same as in Lotus, 

 though differing slightly in details of its mechanism. The weight of the visit- 

 ing-insect depresses the interlocking wings and keel as before ; but the latter 

 is closed only along the anterior margin, so that when it is depressed the 

 stiffer stamens and carpel rise out of the boat-like keel, and come in contact 

 with the lower surface of the insect. The style bears a brush of hairs, which, 

 as it rises, sweeps out the pollen on to the insect's body ; but the stigma reaches 

 its body first, and receives thus such pollen as it may have brought. The 

 flower is elastic and recovers, making successive visits possible. The mechan- 

 ism is less precise than in Lotus, but still very effective. It requires a strong 

 insect, and in absence of cross-pollination self-pollination is possible. 



These examples serve to illustrate the exact mechanism of the Papilionace- 

 ous flower, and the way in which sHght differences may affect the process of 

 their pollination. 



