PEA 29 



the stamens is the pistil, composed of a single carpel. The ovary 

 is green and smooth, and stands horizontally in the trough formed 

 by the united filaments. The style stands almost at right angles 

 to the ovary, occupying the bent tip of the keel. The small 

 stigma at the end of the style is bent so as to point back- 

 wards to the base of the flower. Just below the stigma the 

 upper surface of the style for about one-third of its length is 

 hairy. On opening the ovary a row of ovules will be found 

 attached along the upper edge, where the margins of the carpel 

 joined. 



The complicated structure of this flower, which has been 

 described above without entering into all the details shown in 

 Fig. 8, finds its explanation in the relation of the flower to the 

 visits of insects. To attract these, nectar is secreted around the 

 base of the ovary. The beauty of the complex mechanism can 

 be appreciated, even though in this country the flowers are rarely 

 visited by insects and are normally self-pollinated. To put it 

 as briefly as possible, when an insect strong enough to force up 

 the standard and get at the honey comes to the flower it will 

 depress the wings and keel. On this happening, the style (carrying 

 pollen on the brush of hairs) will emerge from the keel and dust 

 the under surface of the insect with pollen. Should the insect 

 already have pollen on its lower surface, this will be scraped off 

 on the stigma. On the departure of the insect the keel again 

 springs up and encloses the style, so that the process can be re- 

 peated. 



The fruit of the Pea is the pod (see Model Plate at the beginning 

 of the volume), developed from the ovary. This is surrounded at 

 the base by the calyx, and often by the remains of the stamens, 

 but the corolla has fallen off and the style has also withered. 

 The pod can readily be seen to correspond to a folded leaf with 

 the seeds developed from the ovules attached along the joined 

 upper margin. When mature it opens by splitting along both 

 the margin and also the line corresponding to the midrib of the 

 carpel. The large seeds are thus liberated. They have no special 

 means of distribution, but this is compensated for by the large 

 store of reserve material the young plant has to start its growth 

 with. 



