466 



SECOND A RV CHANGES. 



increase exiends lo all the diameters, so that the general form remains, if not exactly, 

 yet approximately, the same. 



The siruciurc of the cambial cells is given in its most important points, by the 



^J-AUj 



-ov, 



a 





:jn%f[M 



^Q 



iff: 



Fig. 199. Fig. 201. 



Figs. 199 — 201. — Fraxinus excelsior. Internode of the stem, two years old, during the winter's rest, beginning of March (375). 

 Fig. 199. Tangential longitudinal section through the layer of the zone of young secondary growth, bordering directly on the mature 

 wood; r medullary rays. — Fig 200. Radial longitudinal section. D, h mature wood , r, <r' limiting layer between this and the young 

 secondary growth : the latter has rows of round pits (shown with too dark an outline) on the radial lateral walls, and passes over on the 

 right into the inner zones of the bast ; r medullary ray — Fig. 201. Transverse section, cc^ hh mature wood of the previous year, 

 shaded ; c — c limit between this and the young secondary growth succeed ng it on the left ; A bast ; r medullary rays. 



Statement of their meristematic properties. They are furnished with densely granular pro- 

 toplasm, and with a well-defined nucleus, which is spindle-shaped, and in the elongated 



