WOOD OF PINUS. 147 



stem ; they are found, however, up to so many as sixteen cells 

 high. They consist of radially-elongated cells, lying side by side 

 in rows. The median cells contain protoplasmic contents, and 

 usually also starch, and show on the sides towards the trachei'des 

 the large shallow unilaterally- bordered pits already noted ; the 

 upper and under rows of cells, from one to three in number, have 

 no protoplasmic contents, contain under natural conditions only 

 water, and are connected with the trachei'des by means of small 

 bilaterally-bordered pits, and also show peculiar jagged or serrate 

 projecting ridges on the walls directed tangentially, which may 

 protect against crushing. Similar rows of cells may also be inter- 

 polated in the median parts of very deep medullary rays ; while 

 there are medullary rays which consist wholly of them, and 

 others which contain none. From their pits and want of living 

 cell-contents these rows of cells resemble, in structure and 

 relations, the trachei'des of the wood, and on these grounds 

 might be considered to be trachei'dal elements of the medullary 

 ray. These trachei'dal elements of the medullary ray probably 

 facilitate water diffusion in a radial direction between the tra- 

 che'ides of the wood ; while the elements which have protoplasmic 

 contents carry reserve food-stuffs in the same directions. The 

 radial longitudinal section may also have cut through a string of 

 secondary wood-parenchyma, and have laid bare its resin-canal. 

 The parenchymatous cells surrounding the resin-canal are convex 

 towards it, and about as broad as long ; those more external are 

 clearly longer. In a larger medullary ray we can perhaps trace 

 the course of a horizontal resin-canal, and possibly see that 

 ultimately the vertical and horizontal resin-canals intercom- 

 municate. 



The cambium in longitudinal section shows on the one hand 

 as narrow elongated cells, with end-walls more or less inclined, 

 in which are protoplasmic contents and nucleus, and from which 

 the elements of the wood and bast proceed ; and, on the other, as 

 shorter, broader, but otherwise similar cells, which are continuous 

 on both sides into the cells of the medullary rays. 



The Bast. In the bast we will specially study the sieve- 

 tubes with their sieve-areas ; and in order to be able to see these 

 latter well and readily, we lay some radial longitudinal sections, 

 which we have prepared from alcohol material, in a watery solu- 

 tion of aniline blue. This stain has, like corallin, the property 

 of deeply staining the callus of sieve-tubes, i.e., the substance 



