EXPLANATION OF THE PLATES 



Fig. 6t Scots Pine, Pinus sylvestris, radial section. Details as in Figs. 4 and 5, but 

 here again we have but one pit in the cross-field. 



Fig. 7. Weymouth Pine. Tangential section showing many small (linear or uniseriatc) 

 rays and one large lenticular ray having in the middle a resin-canal filled 

 with thyloses. Note that the canal occupies the whole of the transverse diameter 

 of the ray (compare Fig. 9), and that the large rays are higher than those of 

 the Larch (and also of the Scots Pine), although the small rays in both species 

 are relatively of the same height. The elongated cells amongst which the rays 

 are imbedded are tracheids. Compare, also, the shape of the lenticular rays in 

 Fig. 9. 



Fig. 8. Larch, tangential section. Details as in preceding figure. Note that the 

 lenticular rays are slender because the greater part of the height consists of 

 one row of cells only. The resin-canal, with its epithelial cells, occupies the 

 whole of the transverse diameter of the middle of the ray (compare Fig. 9 of 

 the Douglas Fir, where there is a row of parenchyma-cells surrounding the 

 epithelial lining which makes the resin-canal appear small). 



Fig. 9. Douglas Fir, Pseudo-Tsuga Douglasii, tangential section. Details as for 

 Figs. 7 and 8, but the lenticular rays are of stouter build. They appear, however, 

 too blunt in the photo as the edge-cells are not shown, but in any case they are 

 of two or more rows of cells for the greater part of their height. The spiral 

 thickenings of the tracheids does not come out. 



Fig. 10. Common Elm, Ulmus campestris, tangential section. The stout oval bodies 

 composed of cells of circular section are multiseriate or compound rays. 

 These have been distorted here and there by strands of fibres passing through 

 them. This form is called "unsymmetrical." The square-ended cells appearing 

 in small quantity, are vertical parenchyma which we may call "muriform," 

 i.e. resembling bricks, as contrasted with the "palisade" in Fig. 12. The light- 

 coloured channels are vessels and the darker elongated cells are wood-fibres. 



Fig. 11. Wych Elm, Ulmus montana, tangential section. Details as for preceding 

 figure. Note that the rays, though of approximately similar height, are narrower 

 and are composed of smaller cells. 



Fig. 12. False Acacia, Robinia Pseud-Acacia, tangential section. The large, wide, 

 white strips are vessels filled with thyloses. The latter are so tightly packed 

 that they become angular in outline. The short-pointed cells in rows are 

 parenchyma "in palisade." The very irregular bodies composed of cells which 

 are round in section are the rays: they are seen in this photo imbedded in the 

 parenchyma. There are but few fibres shown, as the specimen is from the Spring 

 zone of the wood: in the denser wood they form the major part of the tissue 

 whereas the parenchyma is correspondingly scarce. 



CAMBRIDGE: PRINTED BY J. B. PEACE, M.A., AT THE UNIVERSITY PRESS. 



