80 



THE PLANT CELL. 



ii. An internal layer of very thin-walled oelU (endothelial layer) 

 which are full of a granular protoplasm. 



iii. A central cavity, the section across the "duct," in which may 

 be seen globules of liquid resinouS material. This is set free into the 

 duct by the breaking down of the endothelial cells. 



Fig. 63. — A. A FuLLY-FOKMED Resin- 

 canal IN Transverse Section. — 

 en, Endothelial layer ; g, protec- 

 tive fibres ; r, resin-globules. 



B. A Young Resin-canal, show- 

 ing an internal mass of granular 

 secretory cells (en), with as yet no 

 central cavity or duct. — y, Protec- 

 tive-cells. 



Fig. 6-1. — A Resin-canal (r) in 

 THE Xylem of Pinus. — m, 

 Medullary ray. 



In longitudinal section (see Fig. 66) the elements composing 

 the guard-ring are seen to be a variety of sclerenchymatous 

 fibre, and are very thick-walled, with small cell-cavities. The 

 endothelial layer is made out internal to the guard-ring, forming 

 on either side of the central duct a line of parenchymatous cells 

 with granular contents. The development of resin-canals may 



