302 



HOW CEOPS GEOW. 



structure of which, while the cell is young, is shown by 

 a section through them lengthwise. A exhibits such a 

 section through the thickened walls of two contiguous 

 and adhering cells, a;, in both A and B, shows a cavity 

 between the two primary cell-walls ; y is the narrow 

 part of the channel, that 



remains while the mem- 

 brane thickens around it. 

 This is seen at y, as a pit 

 in each cell-wall> or, as 

 Schacht believed, a pore 

 or opening from cell to 

 cell. In ^ it appears 

 closed because the section 

 passes a little to one side 

 of the pore. (Schacht. ) 



In the next figure (54),' 

 representing' a transverse 

 section of the spring wood 

 of the same tree magnified 

 300 diameters, the struct- 

 ure and the gradual form- 

 ation of these §ore-disks 

 is made evident. The sec- 

 tion, likewise, gives an in- 

 structive illustration o f 

 the general character of the 

 simplest kind of wood. R 

 are the young cells of the 

 rind ; G is the cambium, 

 where cell-multiplication ^'S- ^ 



goes on; 1^ is the wood, whose cells are more developed 

 tlie older they are, i. e., the more distant from the cam- 

 bium, as is seen from their figure and the thickness of 

 their walls. At a is shown the disk in its earliest stage ; 

 i and c exhibit it in a more advanced growth. At d the 



