THE TISSUES OF THE STEM 



?7 



In transverse section each cambium cell appears oblong, with the 

 broader sides facing inwards and outwards, while the narrower run 

 radially (Figs. 25, 26, 35). If a section be taken longitudinally 

 through the cambium in a tangential plane, the cells appear with 

 pointed ends interlocked one with another (Fig. 36). If a radial 

 section be taken, so as to follow one of the radial rows, the individual 

 cells will appear long and narrow, with square ends (Fig. 24). 



Cross section through a radial row of 

 cambial zone in Pinus sylvestris, after 

 Sanio. ( x 400.) H=side next the wood. 

 i = the conjectural initial cell. (From De 

 Bary.) 



Fig. 36. 



Tangential section through the cambium of the 

 Elm, showing the elongated form of the prismatic 

 cambium cells. w = thc groups of cambial cells 

 forming medullary rays. ( x 100.) 



Putting together the results of these three sections, the form of the 

 cell as a solid body would be flattened prismatic ; it is placed with 

 its pointed ends directed up and down, and its broader faces inwards 

 and outwards. The cells have very thin walls, and plentiful cyto- 

 plasm, with a large nucleus. In fact they show the characters of 

 embryonic tissue. The cells given off from the initial cell, after 

 further division pass over gradually to the mature state, forming 

 additions to the tissues already present. Those which lie internally 

 are added to the wood, those externallv are added to the bast 



