46 BOTANICAL GAZETTE [JULY 
but always above or below them. Often they are in line with two 
or three degenerating cells on the wood side” (7, p. 112). The 
conclusion seems justified that Abies represents a genus which has 
descended from ancestors which possessed ray tracheids, and is less 
primitive than Pinus. In spite of this, it may sometimes be made 
out in young roots of Abies balsamea that the erect cells have the 
same mode of origin as has been described for Pinus. F ig. 12 
illustrates this point, as well as the fact that the triangular cambial 
cell gives rise to ‘erect cells but not to ray tracheids. In many 
instances the shadowy remains of marginal 
tracheids appear in these root sections. 
With this persistence of marginal cells in 
the phloem may be compared their earlier 
appearance in the phloem than in the 
xylem, as seen in seedlings of Pinus. Just 
why a cambial cell should be more apt to 
cut off segments on the phloem side than 
on the xylem side is hard to say; since the 
supply of food is on the phloem side, un- 
equal nutrition may be the cause at work. 
But it is possible that we must consider the 
phloem to be a more conservative region 
than the xylem, in which case the observa- 
tion has interest from the phylogenetic 
standpoint. The latter view of the case 
is supported by my observations on Ju- 
| niperus, in which genus PeNHALLOWw (4) 


nous with erect cells. 
Species Tray tracheids have 
have been found where 
a border of 
blunt cell ee , ending at the cambium in a 
Judging by the leaves, Jo yt’, tPPearances in Abies balsamea. 
J. virginiana, hence we communis is a more primitive species than 


