THE SPRUCE FIR 



23!) 



sieve-tubes are richer in proteid materials than the rest, 

 and may discharge the function of companion-cells. 



Between xylem and phloem we find a layer of 

 actively dividing cambium, just as in the vascular 

 bundle of a Dicotyledon. Later on, too, divisions take 



, 97. Semi-diagrammatic transverse section of a two-year- 

 old stem of Picea excelsa. b, base of leaf ; pd, periderni ; 

 c, cortex ; r, resin canal ; ph, phloem ; 2 , second year's 

 wood ; tfj, first year's wood ; I, leaf-trace bundle. Magni- 

 fied about 40. (R, S.) 



place in the medullary rays, so as to form an inter- 

 fascicular cambium which completes the ring. Fig. 

 97' shows a transverse section of a twig of the second 

 year, when a good deal of secondary tissue has already 

 been formed. The cambium acts precisely in the same 



