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which ripe pollen is exposed, while the stigmas are yet im- 
mature : still more externally, flowers in which the stigmas are 
mature and exposed, but from which the pollen has mostly or 
altogether vanished, having been carried off by insects. It is 
evident how the different periods of pollen and stigmas in each 
blossom hinder self-fertilisation, and how, on the other hand, 
the close crowding of flowers in different stages, favours inter- 
crossing. 
The common Feverfew will serve as an example. Here each 
disk-flower is furnished with both pistil and stamens. The five 
anthers are united so as to form a tube, closed at the upper end 
(fig. 1), and they dehisce on their inner surface, that is, inside the 
tube. In this latter is lodged the style, which in the yet im- 
mature flower is only so long as just to reach into the lower end 
of the tube with its upper extremity. This extremity is bifid, 
but the two segments are held in close contact with each other, 
there being no room in the tube for them to diverge laterally. 
The stigmas are bends on the borders of the inner surface of 
these segments, and are therefore not exposed to any great ex- 
tent, so long as the two segments are in close contact. At the 
upper end of each segment is a tuft of hair-like papillae, which 
are so set that the whole style, while it is in the tube, somewhat 
resembles a besom with the handle downwards and the twigs 
uppermost. When the flower first expands the pollen is already 
ripe, and lies in that part of the closed anther-tube which is above 
the hairy summit of the style. The style, however, continues to 
grow, and as it lengthens the broom-like end sweeps out the 
pollen cleanly from the dehiscent cells, and, forcing it upwards, 
makes it break open the closed end of the tube and overflow on the 
surface in a confused mass (fig. 2). Hence it is soon removed 
by the insects which crawl over the flower head, and by the 
time that the style itself protrudes from the tube, all or most of 
it is usually already gone. The bifid style now itself emerges, 
and its two segments soon separate from each other and expose 
their stigmatic surfaces (fig. 3). To these a bee can scarcely 
fail to convey pollen from the close adjoining flowers, which lie 
next towards the centre and are less mature. Doubtless, also, it 
will not rarely happen that some of the flower’s own pollen will 
still remain scattered over the petals, and that some of this will 
be conveyed to the stigma and self-fertilisation occur. But 
most of this, and often all, as already mentioned, has already 
gone; whereas the pollen of the more central flowers is yet un- 
diminished in amount. The flower also itself is but one, while 
its less mature neighbours are several, so that the chances are 
largely in favour of intercrossing. This, therefore, and not self- 
fertilisation must be the rule. 
To speak of the tufts of hair-like papillae as collecting pollen 
