ANATOMY AND PHYLOGENY OK THE CONIFERALES. 



even more strikingly double than when it is leaving the central cylinder. The 

 foliar trace continues as geminate strands for ;i short distance! into the base of the 

 leaf; but soon the two fibrovascular bundles become more or less intimately fused. 

 In a section at some height in the leaf, the trace loses all appearance of being 

 a double strand. This is clearly shown in figure ■'!, plate I, which is from a section 

 taken at about the region of the lower third of the leaf of Pseudotsuga douglasii Carr. 

 It will thus be seen that the leaf trace of this species becomes double at an early 

 stage in its progress towards the leaf, and that its double nature only becomes 

 obscured after having penetrated some distance into the lamina. The importance 

 of this observation will be apparent at a later stage. 



The root of Pseudotsuga douglasii m generally diarchous, although examples have 

 been found in which there were as many as three clusters of primary xylem. The 

 primary metaxylem contains no resin canal; but just outside each of the two clusters 

 of protoxylem is a single duct. These features can be seen in figure *2, plate 1. The 

 two first formed resin canals are lined with thin walled, glandular cells, such as occur 

 in the resin ducts of the cortex in the Coniferales in general, and in the ligneous resin 

 ducts of Pinus. The lining of the canals is further particularized by the fact that the 

 cells composing it are quite unlignified and stain a dark bine with haematoxylin. In 

 this respect the tissue in question presents a marked contrast to that lining the later 

 formed ducts of the secondary wood in the root and shoot of the species under discus- 

 sion, which in most cases is thick walled and distinctly lignified. It not infrequently 

 happens that the primary radical resin canals of Pseudotsuga communicate by radial 

 anastomoses with the resin canals of the cortex. The walls of the radial connecting 

 canals in this case are bounded by the same thin walled, resin secreting cells as are found 

 in the ducts which they unite. These radial anastomoses are most frequent in the 

 neighborhood of an outgoing rootlet, but are by no means confined to this position. 

 In figure 2, plate 1, on the left, may be seen one of the radial canals in question. The 

 plane of section does not include the cortical canal into which it opens. In the cortex 

 of both root and shoot of Pseudotsuga are sclerotic cells ; but these do not occur in the 

 phloem as in Tsuga and Abies. 



In figure 1, plate 1, is to be seen a section through a wounded portion of the wood 

 in Pseudotsuga. On the left may be seen the margin of the layer of wound tissue, 

 which is closing over the surface of the injured wood. By following this layer 

 towards the right we reach numerous large resin canals along its inner border. These 

 are traumatic resin ducts such as occur almost invariably in the injured wood of the 

 Abietineae. They are characterized by their number, by the fact that they occur in 

 close tangential rows, the ducts of which generally intercommunicate tangentially, and 



