AUTOGAMY BY THE BENDING BACK OF STYLE-BRANCHES 



363 



of pollen by stigmas from the edge of the anther-tube I observed in several Com- 

 posites, as, for instance, in the species of the genera Adenostyles and Cacalia, and 

 in Arnica montana. The external surface of the style in Adenostyles is beset with 

 papillae, which give it the rough glandular appearance whence it derives its name of 

 Adenostyles ( = glandular style); it has no collecting-hairs, and the pollen is therefore 

 not swept but squeezed out of the anther-tube. The edge of the tube is furnished 

 with prongs, each of which is slightly revolute and is concave almost to the extent 

 of being boat-shaped, so that it is able to retain some of the extruded pollen. This 

 pollen is only used for autogamy in the event of the stigmas not being dusted in 

 any other way. In that case the two style-branches roll back until the receptive 



Fig. 303.— Autogamy effected by means of au intlection of the style-branches. 



, 3 Flowers of Arnica montana in successive stages leading to autogamy. * Style-branches of Arnica in contact shortly after 

 their extrusion from the anther-tube. Pollen is clinging to the collecting-hairs and to the mouth of the tube. * The style- 

 branches projecting still further from the tube and diverging from one another. « The style-branches curved back so as 

 to bring the stigmatic tissue into contact with the pollen sticking to the tube of anthers. ', s, 9 Flowers of Senecio vUcosus 

 in the successive stages of development leading to autogamy, lo A revolute style-branch of Senecio vUcosus with its 

 stigmatic tissue in contact with the pollen sticking to the bristles of the pappus. All the figures magnified. 



tissue comes into contact with the edge of the anther-tube. The style-branches in 

 Arnica montana (see figs. 303 ^' ^' ^' ^' ^' ^) have collecting-hairs on the surface of 

 their slightly-thickened tips only, and in this case the pollen is regularly swept out 

 (figs. 303^ and 303^). A small quantity of the pollen is always left behind upon 

 the 5-toothed edge of the anther-tube. The manner in which the pollen is trans- 

 ferred to the stigmatic tissue by means of the re-volution of the style-arms is shown 

 in the accompanying fiigure 303 ^. 



As illustrations of the abstraction of pollen from the hairs of the corolla we may 

 take a campanulate, a labiate, and two caryophyllaceous species. The corolla of 

 the Nettle-leaved Bell-flower {Campanula Trachelium) has a thick coating of hairs 

 on its inner surface. In the bud these hairs are directed horizontally towards the 

 axis, and touch the style and the anthers. The deposition of the pollen upon the 

 stylar column takes place in the same way as it does in the Bell-flowers already 



