FERTILISATION EFFECTED BY MEANS OF INSECTS. 289 



repeated movement of the keel petal the hairs brush the poUen beyond 

 the anthers on to the stigmatic surface. He found, in many instances, 

 that if the plants were protected from bees, the number of fertile 

 seeds produced was much smaller than when the bees were freely 

 admitted. In the common bean the bees alight on the wing petals 

 (alse), and cause the rectangularly-bent pistil and the pollen to protrude 

 through the slit of the carina. 



In Erica Tetralix each anther-ceU adheres, just in the part where 

 its opening is situated, to the corresponding part of the adjoining cell 

 of the next placed anther in the circlet. Thus the pore of a cell, say 

 the right ceU of an anther, is, so to speak, closed by the pore of the 

 left cell of the next adjoining anther, and so on all the way round. 

 A very little power, however, dislocates the chain of anthers ; a slight 

 pressure on the antherine processes or spurs effects this. An insect 

 accomplishes this easily, and thus its head becomes covered with poUen 

 and applies it to the stigma of another flower. 



Polygala is one of the flowers in which a provision is made for 

 insect fertilising. " The corolla consists of five petals united into one 

 piece and folded in the form of a two-lipped tube. The lower lip has 

 a sort of cup-shaped appendage, with a beard of gland-like bodies ; 

 this lip opens in front by a narrow vertical slit. The filaments are 

 united, and the stamens expand within the cup of the lower lip into 

 a two-lobed membrane crowned by the anthers. The pistil has two 

 stigmas, — one is placed at right angles to the upper side of the style and 

 is perfect, the other is transformed into a spoon-shaped petaloid pro- 

 longation of the pistil reaching to the opening of the lower lip of 

 the corolla, and dividing the interior of the flower into two cham- 

 bers, in the lower of which are the stamens, which are thus separated 

 from the true stigma. The entrance to the flower is closed by hairs 

 pointing outwards and meeting in front, on the mouse-trap principle. 

 A narrow passage is left open above the petaloid stigma. On each 

 side of the interior of the tube of the corolla, above the style and just 

 behind the true stigma, is a group of white hairs pointing down, the 

 tube and meeting above the style. An insect lights on the beard, 

 finds a narrow passage leading over the stigma into the upper chamber. 

 It is prevented by hairs on the coroUa from returning, and is obliged 

 to crawl out through the lower chamber and over the stamens, and 

 thus carries the pollen to other flowers. The calyx, at first tempting 

 to insects, gradually assumes a green colour, and closes over the ripen- 

 ing seed-vessel." (Hart.) 



In Scrophulariacese and Labiatse (figs. 324, 325, p. 207) the axis 

 of the flower is horizontal, and the stamens are approximated beneath 

 the upper lip of the corolla. An insect in passing separates the 

 anthers, and causes the pollen to fall from them, and thus 

 transports it to a more advanced flower. In some Leguminosse the 



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