533 



BOTANY OF THE LIVING PLANT 



the tube of a floret with stigma not yet receptive, the filaments are stimulated ; 

 they straighten and contract, drawing the anther-tube downwards. The 

 bristles of the style thus brush out the pollen at the moment the insect is 

 there, and it is deposited on his body. If he then passes to a floret with stigmas 

 expanded, cross-pollination is ensured. But self-pollination is also possible by 



FIG. 444. 



Head of Dandelion in vertical section. i= involucre, gr = general receptacle. 

 See Text. 



curvature of the stigmas to touch the pollen carried on the stylar brush. 

 These examples show how differences of detail in the florets of the Tubuli florae 

 may be effective in pollination : the fundamental facts being a protandrous 

 condition, and an aggregated inflorescence. 



(ii) Liguliflorae. 



(45) The Common Dandelion, or any Hawk- weed, will serve as an example. 

 The Dandelion (Taraxacum officinale, Web.) is a perennial herb, with massive 

 storage root, a rosette of radical leaves, and solitary, long-stalked heads. 

 The tissues are traversed by branched latex-tubes containing milky-juice. 

 The head consists of an involucre of bracts (Fig. 444, i), seated at the margin 



