20 



EDWARD C. JEFFREY ON 



secondary wood or in the secondary cortex which appear in the figure. Figure 52 

 shows the structure of a three year old root of Tsuga canadensis. There is the same 

 median resin duct as in the preceding figure, but no resin canals appear iu the second- 

 ary wood, the phloem, or the cortex. In figure 5-1, plate 7, is shown a section of a 

 wounded root of T. canadensis. There is a row of resin canals present in the trau- 

 matic wood formed subsequently to the receiving of the injury. The cells surrounding 

 these canals are of the thick walled type, and they often contain considerable tanninifer- 

 ous substance. Figure 55, plate 7, reproduces the structure of the central portion of 

 the primary wood and part of the secondary wood which lies about it. The parenchyma 

 separating the primary from the secondary wood contains a large amount of tannin, but 

 the cells surrounding the resin canal in the center of the primary wood are obviously 

 free from this substance. The resiniparous lining of the median resin canal of Tsuga 

 is thicker walled than in Pseudolarix, Abies, and Cedrus, but its cells are nevertheless 

 quite typical resin-secreting elements. In figure 56, plate 7, is shown the passage of 

 a leaf trace into the leaf in Tsuga mertensiana. The trace is plainly double in this 

 instance, as in the other Abietineae described in this investigation. Bertrand ('74) cites 

 Tsuga as a genus possessing a single leaf trace. If the exit of the trace from the central 

 cylinder be studied in this genus, it becomes evident that the fibrovascular strand is 

 clearly duplicate even before it leaves the wood of the axis, and persists as an obviously 

 geminate strand up into the base of the leaf proper. Tsuga canadensis was examined 

 with the same result, although here the size of the strands of the double trace is some- 

 what smaller. With the description of the leaf trace in Tsuga, the consideration of the 

 recognized genera of the Abietineae, with the exception of Pinus, is completed. In the 

 following paragraphs the bearing of the observed facts on the phylogeny of the order 

 will be discussed. 



Conclusions. 



Having examined from a comparative standpoint the general features of the anat- 

 omy of the Abietineae, we are now in a position to discuss the significance of the facts 

 described, in connection with the affinities and phylogeny of the order. The discussion 

 may conveniently be divided under three heads: (1) The bearing of anatomy in the 

 broadest sense on the interrelationships of the various genera of the Abietineae ; (2) 

 The relationship of the Abietineae to the other groups of the Coniferales ; (3) The affinity 

 of the Abietineae with other groups of Gymnosperms, living and extinct. These will be 

 considered in the order in which they have been mentioned. 



The interrelatio?iships of the Abietineae. — In the foregoing paragraphs it has been 



