THE COURSE OF THE POLLEN-TUBE. 



409 



two delicate featheiy stigmas are inserted (c/. fig. 231, p. 139). The shaft of each 

 of these stigmas consists of elongated, succulent, colourless cells, whilst the barbs of 

 the feather are extremely delicate and filamentous in character, and have the upper 

 extremities of the cells of which they are composed continued as little papillae (fig. 

 313 ^). Neither in the main axis nor in the branches of the stigma are canals present. 

 The cells fit edge to edge, and the pollen-tubes must bore a way for themselves in 

 order to traverse the tissues in this case. The pollen-grains are attached to the 



Fig, 313.— Development of Pollen-tubes. 



1 Longitudinal section of the stigma and upper portion of the style of Lilium Martagon. The pollen-grains present on 

 the stigmatie papillai are sending their tubes down the mucilaginous cells of the style-canal (after Dodel-Port); xllO. 

 2 Portion of the feathery stigma oi Avena elatior. Pollen-grains are attaclied to the papilte, and their tubes may Ije seen 

 boring in between the cells of the stigmatie branches; x 170. 



papillce, and as the little pollen-tubes are produced, these latter bend round so as 

 to grow down along the inner face of the papilla. To do this they often execute 

 very complicated curves, or they may grow spirally round the papillae. Having 

 reached the angle at the base of a papilla, they bore themselves a passage between 

 the superficial cells and grow henceforward down to the ovary in an intercellular 

 channel of their own making. 



In the Grasses not only is no pre-existing canal present, but the cells between 



