36 CHELTENHAM COLLEGE NATURAL HISTORY SOCIETY, 
and exposes the stigmatic surfaces. In Centaurea nigra (Knapweed) 
there is a very remarkable mechanism. The style protrudes so far that 
self-fertilisation cannot take place without the aid of insects, but bees 
visit it in great numbers. The corolla throat is long enough to exclude 
short-lipped insects. When the pollen is shed, and has been swept by 
the style into the upper part of the anther cylinder, a slight touch is 
sufficient to cause the filaments to contract sharply, and this forces 
out a large quantity of pollen. Afterwards the style grows far out and 
exposes its stigmatic surfaces. But it is the wicked that flourish like 
the green bay tree, and the dirty little self-fertilised groundsel is after all 
the most vigorous and persistent foe of every gardener. 
I have only mentioned four orders, and there are others of equal 
or greater interest. I must commend to your notice Zy¢hrum with its 
threefold array of stamens and styles, the Gentians with their blue bell 
developed to attract bees, and then narrowed down to suit the long 
proboscises of the upland Lepidoptera, or the orchids with their 
fascinating multiplicity of devices ; I will now describe the mechanism 
of one or two highly specialised individuals. Lofus corinculatus 
(the yellow trefoil) uses two of its petals to form a “keel,” which 
encloses the stamens and style. Two others form “wings” on 
either side of the “keel,” which are notched into it in such a way as 
to communicate to it any motion they may receive. ‘The fifth forms 
the vexillum, which serves to make the flower conspicuous from every 
point of view. Of the ten stamens, nine are united to form a tube 
round the style, and the tenth forms a guide to the honey, which is 
secreted at its base. The anthers dehisce before the flower opens, and 
the filaments of the stamens expand sufficiently to enclose the pollen 
‘in the cone-shaped end of the “keel.” The ‘‘keel” now grows rapidly, 
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. and five of the stamens expand enormously, forming a pistil which 
completely blocks the cone. When a bee alights on the “ wings” they 
- are depressed, and communicate their motion to the “keel,” and the 
"stamens are consequently forced up the cone, and cause a ribbon of 
pollen to issue forth on to the ventral surface of the bee. In an older 
_ flower the pistil will also protrude, and cross-fertilisation will occur un- 
less the stigma has already been affected by the pollen of its own 
flower. It seems likely, however, that this is not the case, as Delphino 
; concluded that the stigmatic surface was not sensitive until it had 
‘ been slightly rubbed, and this would not happen until all the pollen 
_ had been worn off. 
, In Mimulus and the Musks self-fertilisation is prevented by a 
beautiful device. The stigma is hollow, and the stigmatic surface is 
