175 



STRASBURGER'S NEW INVESTIGATIONS ON THE 

 PROCESS OP FERTILISATION IN 

 PHANEROGAMS. 



By THOMAS HICK, B.A., B.Sc, 



President of the Botanical Section of the Yorkshire Naturalists Union. 

 (Continued from page 159.) 



In his second section Strasburger describes the way in which the 

 pollen-tubes enter the stigma and work their way down the style to 

 the ovary. The section is not a long one, and need not be dealt 

 with in detail. It is shown that there are three or four principal 

 modes in which the entrance of the pollen-tube is effected. The 

 simplest is that met with in species of Lilium, where the pollen-tube 

 grows down between the papillae of the stigma until it reaches and 

 enters one of the three apertures leading into the stylar canal. Down 

 this canal it advances without penetrating any tissue, and so finds its 

 way into the ovary. In Atropa belladonna and other Solanacece the 

 process is scarcely more difficult, though here the pollen-tube 

 advances within the conducting tissue of the style. The latter organ 

 is traversed by a central string of elongated cells, which readily 

 separate into longitudinal series ending in the stigmatic papillas. 

 Between these rows of cells, which form the conducting tissue, the 

 pollen-tubes readily insinuate themselves, and so reach the ovary 

 below. In Cereus speciosissinius a stylar canal is present, but the 

 pollen-tubes do not enter it. On the contrary, they grow down an 

 easily-splitting conducting tissue, which is found in the style, sur- 

 rounding the cavity of the central canal. A somewhat different mode 

 of entrance is met with in Alopecurus pratensis and other Graniinece. 

 Here the stigmatic arms of the style are provided with appendages, 

 which are made up of cells whose upper ends are free and project 

 like teeth. Where appendages are absent, the 'dentition,' so to call 

 it, is provided by the epidermal cells. The pollen-grains emit a 

 single tube each, and this grows until its tip enters one of the angles 

 between the teeth. From this point the further course of the pollen- 

 tube is in the ' middle lamella ' which bounds contiguous cells of the 

 appendages, as, according to Strasburger, observation easily demon- 

 strates. 



Agrostemma githago^ or as it is now called (Hooker: Students' 

 Flora of the British Islands, 3rd Ed.) Githago segetiim, offers a further 

 modification of the process. The five styles are provided on the 

 inner stigmatic surface, with long club-like papillae, each cell growing 

 out into such a papilla at its upper margin. The pollen grains adhere 

 to the surface of the papillae, and produce one or a few tubes. The 



March 1885. 



