144 



X. THE CONIFEROUS STEM. 



longitudinal view. We shall see these connecting resin passages 



again in the tangential longitudinal sections. 



A cross-section through fresh pine- wood (Fig. 53) shows that 



the resin canals are filled with resin. This appears in the pre- 

 paration in the 

 form of strongly 

 refractive viscid 

 drops of often 

 irregular con- 

 tour. If we run 

 in a little al- 

 cohol, the resin 

 drops quickly 

 disappear. We 

 can, moreover, 

 stain them in 

 a characteristic 

 fashion with the 

 red colouring 

 material of alk- 

 anet roots (roots 

 of Alcanna tine- 

 tor ia), which 

 we have already 

 used to colour 



FIG. 53. Part of a cross-section through the wood ot the 

 Scotch fir at the limits of a year's ring. /, spring wood ; s, late 

 wood ; t, bordered pit ; a, a radial row of trachei'des which 

 doubles ; h, resin passage ; m, medullary rays ( x 240). 



oils. For this purpose we take a cross-section through the wood 

 of the Scotch fir, and lay it on the object-slide in a drop of water. 

 We then take a similar thin section from the bark of a dried 

 alkanet root, blow off from it any loose particles, lay it upon the 

 fir section, and cover with a cover- glass. Then run in a drop of 

 about 50 per cent, alcohol under the cover-glass, and allow the 

 object to stand for from half an hour to an hour. If now the 

 alkanet bark is removed and the section of fir examined, the parts 

 containing resin appear stained a beautiful dark-red colour, while 

 the other parts of the preparation remain entirely uncoloured. 



Colour Reactions. Cross-sections, preferably of alcohol material, 

 if treated with chlorzinc iodine show the walls of the trachei'des 

 yellow- brown ; their innermost thickening layer, immediately 

 surrounding the cell-cavity, is, however, here and there stained 

 violet. In the neighbourhood of the cambium, in trachei'des 

 which are not yet fully formed, the protoplasmic contents and 



