4 



EDWARD C. JEFFREY ON 



by the nature of the cells lining their walls. They are apparently for the purpose of 

 sterilizing the wound by pouring large quantities of resin over its surface. Their 

 occurrence in close tangential rows with tangential intercommunication of the ducts 

 is a source of mechanical weakness to the wood, which it is not surprising to hud to 

 some extent overcome by the nature of the cells lining the canals. The resiniparous 

 canals in the case of traumatic resin ducts are lined by thick walled, resin secreting cells, 

 which are able to accomplish their function of pouring out a resinous secretion by the 

 presence of numerous simple pits. 



In the wood of the cone of Pseudotsnr/a doiujlasii Carr., there is a single row of 

 resin canals near the medulla. In longitudinal sections the tracheids of the wood 

 in the female reproductive axis are without the spiral bands, which are a well known 

 characteristic of those of the vegetative axis (Penhallow, '96) . Although tracheids with 

 tertiary spiral thickenings are absent in both the axis and the scales of the cone in this 

 species, they occur in the leaf traces. This would seem to lead to the inference that their 

 absence in the case of the female reproductive axis is rather due to the thickness of 

 the walls of the tracheids in this organ than that the spiral thickenings in question are 

 not a primitive feature of Pseudotsuga. This inference seems strengthened by the 

 fact that the spiral markings are sometimes absent in the case of the thick walled, aes- 

 tival tracheids of the vegetative axis. It does not follow, however, that the occurrence 

 of spirally marked tracheids in the wood of Pseudotsuga is any indication of close affinity 

 with the Taxineae, in which they also occur, since the same phenomenon is sometimes 

 found in the hard pines and in Larix (Penhallow, :03). 



Larix. 



A transverse section of the yearling stem of Larix americana Michx. presents very 

 much the same appearance as one of Pseudotsuga. There is in this genus, however, an 

 absence of the sclerenchymatous elements found in the pith and cortex of the last 

 described genus. The leaf bases, too, are more crowded and more prominent and present 

 a rounded contour. There is as a rule but a single layer of ligneous resin canals and this 

 is present in the summer wood. The root of Larix americana somewhat resembles that 

 of the genus described above, and has the same commissural radial canals connecting the 

 resin ducts, subtending the two clusters of protoxylem, with those which occur in the 

 so called secondary cortex. This feature is shown in figure 6, plate 1. The lining of 

 the resin canals facing the angles of the primary wood is of the same thin walled, resi- 

 niparous cells, which have been described above for Pseudotsuga. The subsequently 

 formed resin ducts of the wood of the root have this thin walled, glandular epithelium 



