60 



THE STRUCTURE OF FLOWERS. 



walls wliicli touch ; so that when they are fully grown the 

 cohesion is firmly secured. An imitative cohesion is seen 

 in the anthers of the Heartsease, which arises from the 

 interlocking of marginal hairs down the sides of the cells. 

 Anthei'S, when thas closely approximate without actual 

 cohesion, are usually called " connivent," as in Ericacece, 

 and the word is perhaps appropriate to those of Solanum 

 Dulcamara ; but in this plant the union is very close, and 

 might even be considered as syngenesious. 



The rationale of the close approximation of anthers, or of 

 actual cohesion between them, is the effect of insect agency, 

 just as for the filaments ; but the method of extraction of the 

 pollen varies. In Viola, the proboscis is thrust through a small 

 orifice between the connectival appendages 

 of the lower pair of stamens, in order to 

 reach the end of the honey-collecting spur. 

 In Heaths and some of their allies, the 

 anther-cells are at first in contact, and so 

 prevent the pollen from escaping ; but each 

 anther is provided with two auricles which 

 extend to the corolla. A bee on entering 

 first strikes the projecting stigma, but its 

 proboscis soon turns one of the auricles 

 aside, which, acting as a lever, dislocates 

 the rest, and a shower of pollen falls out. 

 In Compositce and Lobelia there is a true 

 piston action. The style continuing to elongate drives the 

 pollen out of the cylinder formed by the anthers, and elevates 

 it above the flower, thereby rendering it easy to be dispersed 

 by insects. This is well seen in Centaurea (Fig. 11) ; (a) 

 represents the stamens with tlie anther-cells closed above by 

 the connectival appendages. The arrow shows the direction 

 of the insertion of the proboscis of a bee to reach the annular 



Fig. 11. — Stamens of 

 Centaurea. 



