STEM OP PINUS. 139 



not extend deeply into the woody mass, i.e., the central portion 

 of the stem can be discarded. 



In order that the alcohol material should not become dry, and 

 the elements filled with air, while being cut, it is recommended 

 to lay the pieces required for study in a mixture of equal parts 

 glycerine and alcohol for at least twenty-four hours before they 

 are needed. Material prepared in this way is also much easier 

 to cut, as the hardness which alcohol gives is in great measure 

 rectified. The sections are then examined in glycerine. 



Sections prepared from a stem must be quite accurately 

 directed. We shall need them in three different directions (cf., 

 Fig. 50) ; the cross-section, which must be exactly at right angles 

 to the long axis of the stem, the radial longitudinal section, 

 which must follow accurately the direction of the medullary rays, 

 and the tangential longitudinal section, which must be cut per- 

 pendicularly to the medullary rays. This latter will, of course, 

 only be tangential in a limited sense, and the strictly tangential 

 part of the section must be sought for ; also the thicker the stem 

 the better this section may be. The cross-section must include 

 wood, cambium and bast, and similarly with the radial longitu- 

 dinal section. Tangential longitudinal sections must be taken 

 from at least two parts, one in the wood and the other in the bast. 



In the preparation of these sections the quality and condition 

 of the razor becomes of prime importance. If it be at all blunt 

 the inner thickening layer will be torn from the trachei'des, and 

 the section will be useless. Small sections will suffice, but they 

 must be as thin as they can possibly be made ; and all the 

 precautionary measures already noted must be taken to avoid 

 injury to the razor. If the razor is very hollow ground, correctly 

 directed sections can only be taken from a narrow piece of 

 material, or near the edges of a broader piece ; for only so long, 

 i.e., as the back of the razor does not rest on the cut surface. 

 Hence only slightly hollowed razors should be used for wood 

 sections ; and it would be indeed much preferable to have for 

 this purpose a razor which is ground flat upon one side only 

 (the under one in cutting), but that these razors are difficult 

 to sharpen properly. The surface of the material should be 

 prepared for the razor with a sharp pocket-knife or scalpel, or an 

 old thin-bladed razor may be kept (sharp) for this purpose. Under 

 any circumstances the first sections made should be rejected, as 

 they will include the tissues torn in preparation (see Chap. V.). 



