AUTOGAMY BY THE BENDING BACK OF STY I.K-l'.K \N< II 1>. 361 



is which is devoted to autogamy (see fig. 302 2 ). The process of self-pollination is 

 the last to take place. The two style-branches bend and cross one another, and in 

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

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

 the two style-branches resemble the beak of a cross-bill, as may be seen in fig. 302 8 . 

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

 florets, are always much longer than those of the Asteroidese; 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 grand! flora, 

 Hieracium umbellatum, 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 reminds 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 8. nemorensis and in Centaureas. We will select as an example Centaurea 

 montana (see figs. 302 4 > 5 ' 6 - 7 ), which grows abundantly in the lower Alps. 'Hi-- 

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

 reference 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 point of bifurca- 

 tion of the style. The pollen is swept out of the anther-tube (see fig. 302 4 ) 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. 252). After most of the extruded pollen 

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

 (fig. 302 5 ), 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 

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

 with the pollen left upon the hairs, thus effecting autogamy (see figs. ! 



Bell-flowers (Campanula) exhibit for the most part the same bending back 

 the style-branches, and the phenomenon has the same significance m their 

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

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

 are adjacent to the central column of the style, a* m Composite and fan. | a km I 

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



on the outside of the style, which is furnished with delicate transpar.n 

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



* n f the tube of anthers, but the anthers, after 





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