216 THE FERTILISATION OF FLOWERS. [PART IIT, 
sufficiently long proboscides, alight on the left ala, and in forcing 
the proboscis down into the flower bring its base in contact with 
the stigma. 
Now, when the ale and the carina (which is emer to them) . 
are further depressed, there emerges from the tubular apex of the 
carina, which is coiled nearly into two complete whorls, the 
similarly coiled style; and it emerges in such a way that its 
stigma points downwards and towards the left, and its pollen- 
covered hairs come in contact with the base of the insect’s 
proboscis, dusting it with fresh pollen. In this manner is cross- 
fertilisation insured and self-fertilisation prevented in case’ of 
Fia. 72.—Phaseolus vulgaris, L. 
1.—Flower, viewed obliquely from above and in front. 
2.—Pistil, enlarged. 
a, calyx; 6, vexillum; ec, ale; d, apex of carina; e, ovary; f, style; g, its brush; h, stigma. 
insect-visits; in absence of insects self-fertilisation cannot occur, 
since the stigma protrudes from the carina while the pollen is 
iclosed within it. 
The similar mode of fertilisation in the Kidney Bean (Phaseolus 
vulgaris, L.) was described ten years earlier by Darwin (51), who 
showed by experiment that insect-visits are essential for the 
fertilisation of this plant. Plants covered with a fine net remained 
completely barren, unless the action of bees was artificially 
imitated. When Darwin repeated the experiment on a larger 
scale a few flowers on some specimens bore fruit; small insects 
(Thrips) had presumably gained access to these." 
' Dr. Ogle (No. 633) also gives a thorough description of the floral mechanism 
in P. vulgaris (French bean) and P, coccinea (Scarlet Runner). Of the flowers which 
Dr. Ogle protected from bees by means of a gauze net, no single one bore fruit. 
