THE SPRUCE FIR 



251 



numerable chlorophyll granules, which are embedded 

 in the protoplasm lining the cell-wall (see Fig. 102). 



In the mesophyll we very often find two resin 

 canals placed near the two lateral corners of the leaf 

 (Fig. 1 1 , r). The resin canals have the usual structure, 

 namely, a layer of secreting epithelium next the cavity, 

 and a strengthening ring of sclerenchyma surrounding 

 the epithelium. 

 These resin canals 

 are not very 

 constant in 

 their occurrence. 

 Sometimes there 

 is only one, some- 

 times there are 

 none at all. When 

 present, the canals 

 end blindly at 

 the base of the 

 leaf, so that they 

 do not join on to 

 those of the stem. 

 This shows that 

 the leaf forms its 

 own resin and keeps it to itself. 



We now come to the central cylinder. This is marked 

 off from the mesophyll by a regular endodermis, which 

 has essentially the same structure as the endodermis 

 of a root (see Fig. 103, en). Within the endodermis 

 we find the conjunctive tissue of the cylinder, 

 and in the middle of this is the vascular bundle. 



en. 



FIG. 103. Part of tlie central cylinder and 

 adjoining tissue of the leaf of Picea excelsa, 

 in' transverse section ; from the same sec- 

 tion as Fig. 101, more enlarged, p, cells 

 of assimilating parenchyma ; en, ^ endo- 

 dermis ; t, transfusion tissue of cylinder ; 

 al, albuminous cells; ph, part of the 

 phloem of bundle ; as, part of the xylem 

 of bundle. Magnified 330. (R. S.) 



