EXPLANATION OF THE PLATES 



The scale of magnification is about 50 diameters and is the same for all figures. 



Fig. 1 . Weymouth Pine, Pinus Strolnis : transverse section. A typical Conifer with 

 resin-canals (three only shown). Note the scarcity of these in comparison with 

 the vessels of Broad-leaved woods, such as are shown in Figs. 2 and 3. One of 

 the resin-canals is in the middle zone of the ring. A part of the Spring zone of 

 the succeeding ring is represented by the large-celled portion above. Note also 

 that the cells are strictly in rank and file. The rays are the denser, darker lines 

 running between rows of cells from the top to the bottom of the figure. The 

 resin-canals are lined with epithelial cells: the one towards the right of the 

 figure is filled with thyloses. The cells are flattened on the outer edge of the 

 lower ring, the lumina becoming smaller in proportion to the wall-substance, 

 hence the wood is denser. The contrast between the flattened cells and the lax 

 cells that succeed them, forms a "line of contrast" that serves as the ring- 

 boundary. 



Fig. 2. Birch, Betula alba, transverse section. Pith side downwards. This shows a 

 portion of two rings with a boundary of flattened cells also a number of vessels 

 most of which are in "mother and daughter" groups. Note the relative isola- 

 tion of these groups and their tendency to arrange themselves in oblique lines, 

 and that the vessels of the Spring zone (above the boundary) are larger than 

 those in the preceding Autumn zone (below). There are about 30 groups (in- 

 eluding single pores) shown in the figure. Compare this number with that of 

 the pores in the next figure of the Lime, where it is some ten times as great, 

 and many of the groups have a quite different aspect. The relative transparence 

 of the rays (running from top to bottom of the figure) should be ignored as it 

 is due to the methods of preparation. 



The cells are more or less in rank and file, but they do not show the exquisite 

 regularity of the Coniferous woods. Their density, between that of the Spring 

 (above) and the Autumn (below) wood, does not differ much. 



Fig. 3. Lime-tree. Transverse section. Pith side downwards. A portion of two 

 rings shown, the broadest being above. Compare preceding figure and note 

 that the vessels tend to arrange themselves in loops or undulating lines, rather 

 than in oblique lines and that they are more crowded and larger in the Spring 

 zone than in the Autumn zone adjoining. The cellular tissue (wood-fibres) 

 is relatively dense but the abundance of the vessels counterbalances this, 

 hence the wood is not so heavy as the Birch. 



Fig. 4. Weymouth Pine, Pinus Slrobus, radial section. The long-pointed, vertical 

 cells are tracheids which should show the characteristic bordered pits in this 

 section. The mass of rounded cells (top, middle of photo), are thyloses filling 

 a vertical resin-canal. Immediately below these, the rectangular square-ended 

 parenchymatous lining-cells of the epithelium are seen. The bands of cells 

 passing horizontally across the figure are small linear rays. At the point > 

 where their walls and those of the tracheids form little rectangular spaces 

 (cross-fields) large unbordered pits may be obscurely seen. The zone of narrow 

 tracheids represents the Autumn (Summer) wood: the zone of the wide ones, 

 the Spring wood. 



Fig. 5. Larch, Larix europcea. Details as for previous figure except that there is a 

 horizontal resin-canal, shown in the upper ray and that there are two or more 

 small pits in the cross-fields where they appear as minute dots occupying bat 

 a small amount of the space of the rectangle. 



51 



