[pen hallow] 



A BIRCH ROPE 



241 



traniolecular. Not infrequently the cells show a transverse elongation, 

 indicating a branching -habit of growth which is generally observed with 

 greater clearness in the longitudinal section. 



In the longitudinal section the parenchyma is seen to consist of 

 usually much elongated cells which often become distinctly cylindrical 

 and several times longer than, broad (fig. 3, pr.^ and fig. 4, pr.), but it 

 is also equally clear that these cells constantly diminish in length toward 

 the outer face until they gradually pass into cork (fig. 4, c). The walls 

 are very irregularly thickened, and usually in such a manner that the 



Fig 4. x 250. 



relation of such thickening to mechanical support is quite obvious. The 

 walls are also very generally provided with rather large and frequent 

 pits which are nevertheless often so localized that a given section may 

 not show them, but they appear in part, in figure 4, pt., as also in trans- 

 verse section (fig. 5) where they impart a sieve-plate aspect to the ter- 

 minal walls. Perhaps the most remarkable feature of the parenchyma 

 tissue, is the presence of somewhat definitely organized medullary rays 

 which, though localized, nevertheless show a very well defined relation 

 to the other parts. In the transverse section (fig. 6, r.c.) they are seen 



