1913] HOLDEN—RAY  TRACHEIDS 57 
late. Of the Abieteae, ray tracheids are present normally in Cedrus 
and Tsuga. DeBary (5) and PENHALLOW (6) have both described 
them as characteristic of Abies balsamea, to which DEBARY adds 
_ A. excelsa, but as lacking in other species of Abies. More recently 
THompson has investigated this genus ('7) and found them absent — 
invariably in normal wood, but recalled in a number of species 
as a result of injury. Curiously, he reports them lacking in 
A. balsamea, an observation which I have confirmed from a study of 
seedling, mature wood, vigorous branches, roots, cone axes, etc., 
wounded and unwounded. In Pseudolarix, also, I have been unable 
to find ray tracheids, even in severely wounded branches. Pseudo- 
larix, however, seems to be a particularly unfavorable subject for 
the study of experimental morphology, traumatic resin canals being 
formed much less readily here than in the other members of the 
Abietineae. The only remaining genus, Kefeleeria, has the wood 
structure of Abies. Ray tracheids are entirely absent even in 
such primitive regions as the first annual ring, cone-bearing branch, 
cone axis, and are not recalled after wounding, though there is 
an abundant formation of traumatic resin canals. 
TAXODINEAE 
The Taxodineae as a whole are simpler in wood structure har 
the Abietineae. The resin canals of the latter have disappeared 
here, except in Sequoia (8), their place being taken by resin cells. 
It would be natural to expect that the medullary rays also would 
be simpler, and this is indeed the case. The characteristically thick- 
walled, heavily pitted, parenchymatous ray cells of the Abietineae 
are replaced by thin-walled, sparingly pitted cells, and the ray 
tracheids characteristic of the Abietineae are lacking except under 
certain conditions to be described below. 
The genus Sequoia undoubtedly stands nearest the Abietineae, 
since both living species have traumatic resin canals, and one 
fossil species (9), S. Penhallowii, has abundant pitting on the 
tangential walls of the ray cells, and crystals in the marginal cells 
like those of some species of Abies. Accordingly here if anywhere 
ray tracheids ought to be present, and GoTHan has described them 
as of sporadic occurrence in the old wood of S. gigantea (10). 
