AUTOGAMV BY THE BENDING BACK OF STVI.E-BRANCHES. 3G1 



is which is devoted to autogamy (see fig. 302 -). The process of self-pollination is 

 the last to take place. The two st3de-branches l)eud and cross one another, and in 

 so doing bring the pollen adhering to the lower hairs of the one arm into immediate 

 contact with the receptive tissue on the margin of the other arm. In this position 

 the two style-branches resemble the beak of a cross-bill, as may be seen in fig. 302 ^. 

 The style-branches of tliose Composites whose capitula consist entirely of ligulate 

 florets, are always much longer than those of the Asteroideee; they are of thread-like 

 appearance, and the lower parts of their external surfaces are beset with collecting- 

 hairs. In one section of these Composites, including, for instance, Crepis grandiflora, 

 Hieracium umbellatitm, and Leontodon hastile, there is likewise, shortly before the 

 flowers fade, a simultaneous inflection and spiral involution of the two branches of 

 the style resulting in autogamy; it i-eminds one, even more forcibly than the case 

 of Asteroidese, of the action of a person when he crosses his arms. 



The second kind of process, viz. the spiral re-volution or bending back of the 

 style-branches, may be particularly well seen in the Groundsels — Senecio Fuchsii 

 and S. nemorensis — and in Centaureas. We will select as an example Centaurea 

 viontana (see figs. 302 *■ ^' ''■ '), which grows abundantly in the lower Alps. The 

 styles are fashioned quite differently from those of the composite flowers to which 

 refei'ence has been made above. The stigmatic tissue is spread out over the inner 

 surface of the style-branches, especially over the part near the free extremity, and 

 the collecting-hairs are confined to a narrow zone underneath the jjoiut of bifurca- 

 tion of the style. The pollen is swept out of the anther-tube (see fig. 302 *) in the 

 same manner as in the other Composites, but in Centaurea the process of extru- 

 sion is accelerated by a sudden contraction of the irritable filaments of the stamens 

 when they are touched by insects (cf. p. 2.52). After most of the extruded pollen 

 has been removed by insects or scattered liy the divergence of the style-branches 

 (fig. 302 °), the receptive inner faces of the latter are so disposed as to ensure cross- 

 pollination in the event of insects coming laden with pollen from other capitula. 

 This state of affairs, however, only lasts a .short time; the two style-branches soon 

 roll back and bring the receptive tissue of their originally inner faces into contact 

 with the pollen left upon the hairs, thus effecting autogamy (see figs. 302^ and 302^). 



Bell-flowers {Campantda) exhibit for the most part the same bending back of 

 the style-branches, and the phenomenon has the same significance in them as in 

 composite flowers, but the manner in which the pollen is transferred to the external 

 surface of the style is somewhat different. Within the closed bud the long anthers 

 are adjacent to the central column of the style, as in Compositffi, and form a kind of 

 tube round it. These anthers open inwards, too, and deposit the whole of their 

 pollen on the outside of the style, which is furnished with delicate transparent 

 papillre, and is in consequence well adapted to the retention of the pollen. The 

 pollen is not, however, swept out of the tuVie of anthers, but the anthers, after 

 depositing their pollen upon the stjdar column, separate from one another and 

 shrivel up, and only persist as shrunk and empty relics at the bottom of the flower 

 (see fig. 302 ^). The style-branches are by this time divergent, and occupy a posi- 



