PHYSIOLOGY OF THE FLOWEE. 12J 



and the weight of the insect effects more or less disarrangement 

 of parts. There are four chief ways of action : — 



(i.) In birds-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.) Siveet 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 flowers are 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 monad elphous, 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, upon 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. Violet 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 



