ANATo.mv WD PHYLOGEN? OF THE CONIFERALES. 



5 



more or less completely replaced by thick walled, resiniparous cells, which are at least 

 partially lignified. There are, however, nearly always some of the more primitive, thin 

 walled cells remaining. The radial canals connecting those opposite the primary wood 

 with similar canals in the secondary cortex have their inner surface also lined with the 

 thin walled type of gland cells. In the stem of Larix, as has been pointed out by Pen- 

 hallow ('96, :03). the resin ducts of the wood are coated with thick walled, resiniparous 

 cells, presenting in this respect a marked contrast to Pinus. 



The leaf trace of Larix is described by Bertrand (74) as resembling that of Tsuga 

 and Pseudotsuga in remaining a simple undivided fibrovascular strand. An examination 

 of thin sections through the yearling stem of Larix americana has shown that the foliar 

 trace here is also double, as in Pseudotsuga described above. The trace sometimes shows 

 indications of duplication even before it leaves the central cylinder of the axis, but gen- 

 erally does not become double until it has advanced some distance into the cortex, in its 

 upward course into the leaf. Figure 7, plate 1, shows the condition of the leaf trace at 

 about the level at which the resin canals of the mesophyll have made their appearance. 

 As is well known (Strasburger, 71) , the resin ducts of the fundamental tissues of the leaf 

 in the Abietineae are not generally continuous with the similar canals of the cortex of the 

 axis. At this height the leaf trace as seen in transverse section is obviously double, the 

 tracheary strands being separated from each other by two or three rows of parenchyma 

 cells. These two fibrovascular bundles become intimately fused in the base of the free 

 portion of the leaf, and it is no longer possible to distinguish any signs of duplication. 



Picea. 



In Picea nigra Link, a section of the yearling stem shows the presence of abundant 

 sclerification in the pith. Sclerenchymatous strands are also present in the cortex, sub- 

 tending the outgoing leaf traces. The woody cylinder normally contains but a single 

 row of resin canals which are nearly midway between the beginning and the end of the 

 annual ring. These canals differ somewhat from those of Larix in their lining, for their 

 parietal glandular tissue is partially thick walled and partially made up of thin walled 

 elements. The latter are always present to some degree and no doubt are responsible 

 for the formation of the tyloses which occur in the canals of Picea, in contrast to those 

 of Larix, where both tyloses and thin walled elements are for the most part absent. 

 The leaf bases of Picea are sharp pointed instead of rounded in transverse section, as is 

 the case in Larix. They are further particularized by the presence of two small resin 

 canals, which in the mature stem end blindly upwardly, although they are inferiorly in 

 communication with the much larger resin canals of the cortex of the axis. As Mayr 



