2 



EDWARD C. JEFFREY ON 



fullness which makes them of the greatest value in the interpretation of the phylo- 

 genetic relationships of the existing Gymnospermous groups. Extremely important 

 results have been obtained in recent years by the anatomical method, in the case 

 of the Ginkgoales and Cycadales; but the Coniferales can scarcely be considered 

 to have been properly investigated in the light of recent additions to our knowl- 

 edge of the structure of the Cycadofilices, Cordaitales, and other ancient and tran- 

 sitional groups. This statement is made because investigations of recent date on 

 the Coniferales either do not concern themselves with a consideration of the fossils 

 at all, or are devoted to some special theme, such as the structure of the wood, 

 the anatomy of the leaf, etc. Modern work on the anatomy of plant fossils empha- 

 sizes the fact that all the organs and tissues should be examined, where successful 

 comparisons are to be made. It will accordingly be the aim of the present investi- 

 gation to include all the structural features of the Abietineae, so far as they seem 

 to have any bearing on the phylogeny of the order. 



PSEUDOTSUGA. 



In a transverse section of a vigorous yearling shoot of Pseudotsuga douglasii 

 Carr., one sees the comparatively thick fibrovascular ring surrounded by a thick 

 cortex. The wood of this genus is characterized by the presence of resin canals 

 of which there are generally present about three rows. Occasionally one finds shoots 

 in which the resin ducts of the wood are quite absent. The pith is irregular in 

 outline, on account of the occurrence of projections from its periphery correspond- 

 ing to the outgoing leaf traces. These rays of medullary parenchyma become deeper 

 and deeper as the leaf trace passes outwards from the medullary crown towards 

 the cortex, and where the trace is about to leave the fibrovascular ring there is a 

 radial stripe of parenchyma several cells broad extending entirely through the woody 

 cylinder. This is the foliar gap. Very shortly after leaving the medullary crown, 

 the leaf trace becomes divided into two by a radial row of parenchyma cells, which 

 as the trace begins to approach the outside of the woody cylinder, becomes two and 

 even three layers of cells wide. One or both of the leaf traces at this time may 

 contain a resin canal, which disappears as soon as the trace begins to pass into the 

 phloem. Figure 4, plate 1, shows the topography of the passage of the foliar trace 

 out of the central cylinder and demonstrates that it is distinctly double. It is 

 important to note this point because Bertrand ('74) states that Pseudotsuga, together 

 with Tsuga and Larix, is characterized by a single undivided leaf trace. In figure 5, 

 plate 1, the leaf trace is seen at some distance out in the cortex, and is obviously 



