THE TREE ITS SHOOT-SYSTEM 101 



to side, and therefore stands out like a knife, with an 

 upper and a lower edge (fig. 27). 



Now imagine the primary vascular bundles replaced. 



FIG. 27. Tangential longitudinal section of oak wood, 

 magnified fifty diameters, and showing the transverse sec- 

 tions of the medullary rays, cut as they project towards 

 the observer. (Miiller.) 



The first change is that the cambium in the vascular 

 bundles becomes continuous across through the medul- 



