THE PRINCIPLE OF ADHESION. 81 



la the case of Orocus, Convolvulus, and other flowers with 

 a contracted base to the corolla or perianth, the anthers are 

 situated close round the style. In these flowers, tlie insect 

 alights on the stigmas, as already described, grasps the central 

 column and sucks the honey head downwards, and so gets 

 dusted on the abdomen, the pollen from which is thus trans- 

 ferred to the next flower visited. 



The adhesion of the stamens to the corolla or perianth 

 thus seems to give a rigidity and firmness, as well as leverage 

 in some cases, so that the action of the insects is more 

 accurately secured, and some one particular spot on their 

 bodies invariably struck and dusted with pollen ; which 

 would scarcely be the case if the filaments were free and at 

 liberty to oscillate or swing about in any direction. 



In many flowers with irregular corollas, the stamens are 

 declinate ; and their adhesion to the tube is then of manifest 

 advantage, for the basal part of the filaments thus acquires an 

 additional strength to act as a fulcrum, which enables the 

 filaments to support the weight of the insect. In Echium, for 

 example (Fig. 20, p. 82), the corolla is even strengthened by 

 a rib where the stamen is inserted. This part constitutes the 

 fulcrum. The line of force from the fulcrum intersects a line 

 perpendicular to the filaments, corresponding to the weight of 

 the insect ; while the third and upward force is that exerted 

 by the filaments to counteract the resultant of the two former.* 



The origin of the adhesion between the stamens and the 

 outer whorls is revealed by anatomical investigations ; for 

 the rule is, as described in the case of Prunus, that the fibro- 

 vascular cords of the stamens arise by division from those of 

 the outer whorls whenever they are superposed to them. 



In other words, when adhesions are seen between the 

 floral whorls, by being superposed to one another, then a 



• See also Figs. 38, 39, and 40, pp. 124-126, and consult text. 



