BORDERED PITS. 



75 



The razor must be as sharp as possible, otherwise it will tear the 

 cell-walls, and separate the inner thickening layers from the 

 outer. The wood preserved in alcohol cuts more easily than when 

 dry, especially if the former has been laid for about twenty-four 

 hours prior to use in a mixture of equal parts glycerine and 

 alcohol. The surface which has been prepared by the pocket- 

 knife, since it contains the torn cell-walls, must be removed 

 with the razor in sections as thin as possible, and rejected. The 

 succeeding sections can be used. 1 



A radial longitudinal section, rightly directed through the 

 wood of the Pine, appears, with weak magnification, to be com- 

 posed of longitudinally elongated cells, which overlap one another 

 with their tapering, rounded ends. Running across these cells 

 we see the cell-rows of the medullary rays, with which we shall 

 not at present concern ourselves. We focus now with a higher 

 power upon a part in which we see only the walls of the longi- 

 tudinally elongated wood-cells, always selecting the broader of 

 them, and concentrate our attention upon the bordered pits of 

 these walls. The bor- 

 dered pit appears in n 

 the form of two con- 

 centric circles or ellip- 

 ses (Fig. 27, .4). The 

 inner small circle, or 

 ellipse, represents the 

 opening of the pit into 

 the cavity of the cell ; 

 the larger outer circle, 

 or ellipse, the broadest 

 part of the pit, with 

 which it joins on 

 to the primary wall 

 separating the two 

 elements. This pit, therefore, is only distinguished from the 

 simple pit, as we have seen it in the Date and in Ornithogalum, 

 in that it broadens at its base. The pits of the adjoining cells, 

 however, coincide here in just the same way. If the mouth of 



1 It is of some advantage to keep an old thin razor (sharp, however), for 

 preparing surfaces, as it is keener than a pocket-knife, and will spare the 

 actual section razor. Even then the first section cut with the latter should 

 be rejected. [ED.] 



FIG. 27. Finns sylvestris. A, a bordered pit in sur- 

 face view ; B, a bordered pit in tangential longitudinal 

 section ; #, the torus. C, cross-section of an entire tra- 

 cheide ; //?. middle lamella: /*, a "seam"; i, the 

 limiting membrane ( x 540). 



