1915] BURLINGAME—ARAUCARIANS 25 
tinean cone and in certain fossil forms, resin canals are not actually 
a character, as JEFFREY maintains (42), of the ancestors of modern 
Abietineae, and much less so of the ancestors of modern araucarians. 
The absence of ray tracheids from the seed cone of Pinus and 
of the erect cells of the phloem from the cone and first few years’ 
growth of the stem and root (13, 70) is interpreted to mean 
that these structures have been acquired in the comparatively 
recent geological history of the group, very probably long since 
the time at which Araucarineae are supposed to have originated 
from it. 
In the outer extremities of the vascular bundles of the leaf of 
the Araucarineae there is a considerable amount of centripetal 
xylem. It has been interpreted in various ways. THOMSON holds 
that, though much of it is of the transfusion type, there is yet 
always a certain number of elongated elements that are true cen- 
tripetal wood lying next the protoxylem (70). 
Attention has often been called to the fact that seedling pines 
have only primary needle leaves and only later develop spur shoots. 
If they are ancestral to araucarians, the latter might be expected 
to develop spur shoots on the seedling. 
Traumatic reactions play little part in THOMSON’s argument, 
though he does invoke its aid in the attempt to show that the 
ancestral type of resin canal (70) in the pines was solid. He points 
out that the resin canals produced by wounding modern pines are 
much more numerous than can reasonably be expected to have 
been the case in the ancestral forms, and that they are frequently 
solid. The argument would appear to cut both ways. In a 
later paper (73) he has studied the normal variability of the spur 
shoot of Pinus and has made free use of the effects of wounding 
to substantiate his conclusions. His general conclusions are that 
the larger numbers of leaves on the less definite spurs of fossil forms 
find their counterparts in the normal variations in the number of 
leaves to a fascicle of living pines, particularly such wide variations 
as occur frequently on very vigorous branches, on reproductive 
axes, and on vigorous seedlings. Variation in the number of needle 
leaves, branching of the spur shoot, the production of primordial 
leaves on branches, and even on proliferating spur shoots can all 
