PHYSIOLOGY OF THE FLOWER. 127 
and the weight of the insect effects more or less disarrangement 
of parts. There are four chief ways of action :— 
(1.) In bird’s-foot trefoil and lupin the pollen collects in the 
end of the keel, and when an insect alights, some of it is forced 
out and the stigma is also protruded. 
(2.) Clover presents similar features, but the stamens are pro- 
truded as well. | 
(3.) Sweet and everlasting peas, broad bean, and scarlet runner 
possess a style which presents a hairy region near its end, the 
use of which is to sweep out pollen. The stigma is also protected 
by hairs from self-pollination. 
Scarlet runner is the most complicated, and here the keel is 
drawn out into a narrow spiral “snout,” occupied by the similarly 
curved style and stamens. The pressure of a bee on the wings 
causes the oblique stigma, protected by a circlet of hairs, to be 
protruded, and then the hairy part of the style with its attached 
pollen grains. 
The seven flowers just described all recover their normal shape 
when the insect leaves, but in (4.) broom and gorse the newly- 
opened flower is in a state of tension. The pressure of a bee 
causes it to “explode,” as the projections at the bases of the 
petals are unlocked from the corresponding depressions. 
Where the stamens are monadelphous, as in lupin, broom, and 
gorse, pollen only is afforded. The remaining flowers named 
above excrete nectar on the inner side of the staminal tube, and, 
as the upper stamen is free, this can readily be reached from 
above. 
Pansy (fig. 51) recalls the heath, in that it presents a special 
arrangement for dusting its visitors. Here the base of the style 
is slender and bent, while the stigma is dilated, hollow, and pro- 
vided with a receptive lip facing downwards. The anthers with 
their triangular appendages closely surround the style, leaving, 
however, a space between them and it, which receives the shed 
pollen. If an insect now alights on the lower petal, its proboscis, 
when thrust into the spur, must touch the stigma-lip, wpon which 
it leaves pollen if other flowers have been previously visited. At 
the same time the insect’s head will push against the head of the 
stigma, causing the slender style to bend and pollen to fall out. 
The proboscis when drawn out folds up the stigma-lip (cf. iris), 
and any grains that happen to be on it at once adhere to the 
sticky fluid with which the stigma is filled. V7olet is similar, but 
the stigma is shaped differently. 
We are now in a position to understand why the posterior 
stamen is aborted in so many irregular flowers (cf. p. 94). The 
style is thus enabled to occupy the upper side of the corolla, out 
