THE SPRUCE FIR 



2G1 



(see Fig. 107). The limit between plerome and 

 periblera is often impossible to trace near the apex. 

 Thus in our figure the sharp line of demarcation at p 

 corresponds to the limits of the pith, not to those 

 of the plerome. Without entering further into the 

 question of the meristematic layers, which is a difficult 

 and disputed one, we may safely say that their differ- 



FIG. 107. Median longitudinal section of the growing point 

 of the stem of Picea excelsa. a, apex ; I, I, very young 

 leaves ; p, p, young pith ; c, c, cortex. Between c and 

 p the vascular bundles arise. Magnified about 140. 

 (After Sachs.) 



entiation at the apex of the stem is on the whole less 

 sharp in Gymnosperms than in Angiosperms. 



The leaves and branches arise, just as in Angio- 

 sperms, exogenously, i.e. they are formed entirely by 

 the growth and division of cells which belong to the 

 outer layers of the meristem (see Fig. 107, 1, 1). Their 

 tissues are always in direct continuity with those of 

 the shoot which bears them. 



/3. Growing Point of tJie Root 



The apex of the root in the Fir and its allies grows 

 in much the same way as that of a Dicotyledon. 



