146 



X. THE CONIFEROUS STEM. 



wood the closing membrane round the torus sometimes shows 

 radial striation (Fig. 27 A). The torus can be shown up clearly 

 if the section is laid for about fifteen minutes in Bohmer's log- 

 wood solution, or in haern-alum ; but sections taken from alcohol 

 material must previously lie for a little while in water in order 

 that no precipitate of logwood be formed on the surface. In the 

 narrow late summer tracheides the bordered pits are small and 

 less numerous. 1 



sm 



FIG 54,. Radial longitudinal section through the stem of the Scotch tir, at the outer 

 limits of the xylem, through the cambium, and the adjoining bast, and showing 

 also a medullary ray. s, autumnal trachei'de ; t. bordered pit ; c, cambium ; 

 v, sieve-tube ; vt, sieve-area ; tm, trache'idal medullary-ray cell ; sm, starch - 

 containing medullary -ray cell in the xylem ; sm 1 , in the phloem ; em, proteid- 

 containing medullary-ray cell (x 240). 



Traversing the tracheides horizontally we see the cells of the 

 medullary rays (Fig. 54, sm}, the structure of which we can 

 study more readily now than in the cross-sections. The medul- 

 lary rays usually have but little height, i.e., in the direction of 

 the length of the tracheides and therefore of the length of the 



1 It would be well for the student also to refer back to the section on 

 " Bordered pits of Pinus " in Chap. V., as some further details are to be found 

 there. [ED.] 



