152 



X. THE CONIFEROUS STEM. 



attention. We can easily follow on the one side their enlarge- 

 ment, and on the other side their disappearance. 



The resin-canals which 

 we have here met with, and 

 which in the cortical paren- 

 chyma of Conifers often attain 

 very considerable size, can 

 have their origin well studied 

 in the Ivy (Hedera helix). 

 Cross-sections of young stems 

 will show the resin-canals in 

 the central pith as well as 

 outside the xylem ring, even 

 in quite close proximity to the 

 cambium ring. In the same 

 section they will be met with 

 in different stages of develop- 

 ment, from a group of four 

 cells, having between them a 

 barely recognisable intercellu- 

 lar space, to fifteen or twenty 

 ^ . w ^ cells surrounding a large 



Fig. 57*. Resin-passages in the bast of a Cavity. The cells are at 



young stem of Hedera helix in transverse sec- _ ui n 



tion (x 800). 'A, early stage ; JS, later stage ; Once recognisable by their 



ff, the resin-passage surrounded by its secret- granular contents. The mode 

 ing cells ; c, the cambium layer ; tvb, soft ' . . 



bast ; b, bast fibres ; rp. cortical parenchyma. Of Origin of the resin-passage 



is easily observable. It arises 



through the separation of the secreting cells, while these cells 

 divide radially, and more rarely tangentially (Fig. 57* A), and 

 thus surround a cavity continually enlarging up to a certain 

 point. The resin-passage, therefore, as in Pimis, is schizo- 

 genous (compare Fig. 57*). 



