376 



HUTCHINSON'S POPULAR BOTANY 



FIG. 463. ASPIDISTRA. 



Section of flower, showing sessile 

 anthers and mushroom-like stigma. 



the corolla-tube elongates, and by that means its 

 sessile anthers, which form a circle on the interior 

 surface of the tube, are rubbed against the knotted 

 stigma (fig. 454, c). In the Forget-me-not (M. 

 palustris) anthers and stigma are on a level, so 

 that self-pollination is sure to take place in the 

 absence of insects (fig. 454, d). 



Take the Common Groundsel (Senecio vulgaris), 

 again. It is one of the Composites, and each of 

 its capitula bears from sixty to eighty inconspicu- 

 ous tubular florets, which vary in length from one- 

 tenth to one-eighth of an inch. Marginal or rayed 

 florets, which might serve to attract insects, it has 

 none, and hence, though the honey is easily ac- 

 cessible, the plant seldom gets visited. In this 

 case, therefore, self-pollination takes place almost as a matter of necessity. 

 The styles are furnished at their tips with tiny brushes, which sweep out the 

 pollen-grains in a most effectual manner, holding them fast to the edges of 

 the stigmas, into which the delicate tubes push their way. 



Perhaps such diminutive flowers as those of Myosotis and Groundsel are 

 not the best examples that might be chosen to illustrate the facts before us, 

 and it will be helpful to name a familar flower of larger growth, which, 

 though normally cross-fertilized, occasionally pollinates itself. Such a flower 

 is the well-known Garden Convolvulus (Ipomoea purpurea, fig. 457). "Whilst 

 the flowers are young," says Darwin, " the stigma projects beyond the 

 anthers, and it might have been thought that it could not have been 

 fertilized without the aid of humble-bees, which often visit the flowers: 



but as the flower grows older the sta- 

 mens increase in length, and their 

 anthers brush against the stigma, which 

 thus receives some pollen." Its action, 

 indeed, resembles that of Myosotis versi- 

 color, save that the bringing of the 

 anthers to a level with the stigma is 

 effected by the lengthening of the 

 stamens not of the corolla-tube. 

 Kerner asserts that the process of au- 

 togamy or self-pollination in Ipomosa, 

 is further facilitated by the involution 

 of the corolla, which occurs at the close 

 of flowering, whereby the anthers coated 

 with pollen are pressed against the 



FIG. 464. OXLIP (Primula elatior). stigma. 



(a) Pin-eyed and (b) Thrum-eyed flowers. Self-pollination by means of the 



