568 



PHANEROGAMS. 



ovary (as in Fragaria and Alchemilla). If this occurs with each of the carpels of a 

 polycarpellary ovary, the ovary itself appears to be depressed in the middle, and the 

 style rises from the depression (Figs. 387, 388). In Labiatae and Boragineae this 

 peculiarity is especially conspicuous, the four lobes of the bilocular ovary forming 

 strong protuberances (Fig. 390, A, B\ so that the style finally appears to spring 

 from between four parts of the ovary which seem to have scarcely any connection 

 with one another, and is hence termed a gynobasic style. 



The style may be hollow, that is, it may be penetrated by a channel consisting 

 of a narrow elongation of the cavity of the ovary, as in Butonius (Fig. 382, B, F), 

 where it opens on the hairy surface of the stigma; or in Viola (Fig. 395), where 

 the channel is broad, and opens above into the spherical cavity of the stigma ; 

 or in Agave and Fourcroya, where the style is hollow throughout its whole length 



and open to the stigma, the simple channel dividing 

 below into three tubes which run into the loculi of 

 the ovary, a phenomenon which occurs also in other 

 Liliaceae\ In other cases it is at first hollow, as in 

 Anagallis (Fig. 392, B), but becomes 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,' through 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 Iridese it generally attains 

 a considerable size ; in Crocus it is very long, tripartite 

 above, each division being 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 appearance of 

 being a mere constriction between the ovary and stigma, as in Viiis. 



The Stigma '^^ in the narrower sense of the term, is the part of the style which 

 is destined for the reception of the pollen. When pollination takes place it is 

 covered with a viscid secretion, and usually with delicate hairs or short papillae, 

 constituting a glandular structure which is sometimes merely a peculiarly developed 

 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 explained only when these facts are taken into consideration. A few 



Fig. 395. — Lonsritudinal section througli 

 the ^ynfficeuni of Viola tricolor ; SA' the 

 anatropous ovules, ,^/i channel of the style, 

 o its opening : in the hollow of the stigma 

 which is filled with the stigniatic secretion 

 are pollen-grains which are putting out their 

 pollen-tubes. 



* Zuccarini, Nova Acta Ac. Leopold, XVI. pt. II. p. 665. 



^ [Behrens, Untersuch. ueb. d. anat. Bau des Griffels und der Narben, Gottingen 1875.] 



