ANGTOSPEEMS. 



499 



afterwards filled up by the growth of the tissue. There is usually no channel to be 

 detected in the style when the pistil is ready for fertilisation, or at least not in its 

 upper part ; in the place of this its centre is occupied by a mass of loose tissue 

 the 'conducting tissue,' down which the pollen-tubes grow till they reach the cavity 

 of the ovary. The external form of the style is usually cylindrical, filiform, or 

 columnar, sometimes prismatic or ribbon-shaped ; in the Irideae it generally attains 

 a considerable size ; in Crocus it is very long, tripartite above, each division beino- 

 deeply hollowed out like a cup ; while the genus Iris is distinguished by its three 

 free broad petaloid coloured styles. Sometimes the portion of the style which 

 belongs to each carpel branches, as in Euphorbiaceae, where a tripartite style, each 

 arm of which bifurcates, corresponds to the three carpels. The style frequently 

 remains very short, and then has the appear- 

 ance of being a mere cons^triction between the 

 ovary and stigma, as in Vitis. 



The S/igfJia, in the narrower sense of the 

 term, is the part of the style which is destined 

 for the reception of the pollen. When pollin- 

 ation takes place it is covered with a viscid 

 secretion, and usually with delicate hairs or 

 short papillcc, constituting a glandular structure 

 which is sometimes merely a peculiarly de- 

 veloped portion of the surface of the style, 

 sometimes a special organ of very variable ap- 

 pearance attached to it. The form of the 

 stigma always has an intimate connection with 

 the mode of conveyance of the pollen by insects 

 or otherwise, and can be understood and ex- 

 plained only when these facts are taken into 

 consideration. A few specially interesting cases 

 will be described in Book III ; it is sufficient 

 now to mention that the surface of the stigma 

 forms the exit of the open channel of the style 



when there is one ; if this channel is closed or entirely absent, the stigma has the 

 appearance of a superficial glandular structure upon or beneath the apex of the 

 style or of its arms. If these arms are long and slender, and covered with long 

 hairs, the stigma has the form of a pencil or tuft of hairs or feathers, as in Grasses ; 

 in Solanaceae and Cruciferce the moist surface of the stigma covers a knob-like 

 indented thickening at the end of the style ; in Papaver it forms a many-rayed 

 star on the lobed style. Sometimes the stigmatic portion of the style is greatly 

 swollen, as in the Asclepiadese, where the two monocarpellary and distinct ovaries 

 cohere by the stigmas; the true stigmatic surface into which the pollen-tubes 

 penetrate lies in this case concealed on the under side of the stigma \ 



Fig. 364.— Longitudinal section through 

 the gyna?ceum of Viola tricolor ; SK the 

 anatropous ovules, ^h channel of the style, 

 o its opening- : in the hollow of the stigma 

 which is filled with the stigmatic secretion 

 are pollen-grains which are putting out their 

 pollen-tubes. 



1 On the position of the lobes of the stigma in relation to the placentae in different plants, see 

 Robert Brown, Misc. Bot. Works, Ray Soc. 1867, vol. I, pp. 553-563- 



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