365 
on the Genus Drimys. 
degenerate vessels with the similarly organized scalariform elements of the 
primary wood the question of interpretation becomes difficult. The situa- 
tion, therefore, may be compared somewhat accurately with that in Sequoia 
• temper virens. In this species resin canals are formed as a result of injury, 
and do not, as in the allied species .S. gigantea , occur in the primitive 
regions — first annual ring, leaf trace, and cone axis and its scales. Trau- 
matism in the redwood (S. sempervirens ) supplies, in fact, the only evidence 
as to its former possession of resin canals, while in the big tree (S. gigantea) 
traumatic evidence is reinforced by the conditions found in the conservative 
organs. The situation in Drimys may also be compared quite accurately 
with the wood phenomena presented by the rays of the Taxodineae and 
Cupressineae in general as described by Miss Holden 1 and one of us . 2 
Here the return of ray tracheides has been observed only as the result 
of injury, and is not found normally in any of the regions recognized as 
conservative. 
But if it be granted that the vessel-like structures which occur trau- 
matically in the injured root are distinct evidence of the former presence of 
vessels in Drimys , we have still certain difficulties to consider. First, there 
arises the question whether the structures under discussion are in reality to 
be regarded as degenerate vessels in reversionary return. Secondly, there is 
the equally important problem as to whether it is inherently probable that 
any group or genus of Angiosperms can primitively have possessed vessels 
and have subsequently lost them. 
Taking the question of interpretation .first, we may ask if the peculiar 
scalariform elements occurring in the root of Drimys after injury are in 
reality to be interpreted as of the nature of vessels. They are certainly not 
to be considered as tracheides, since the sculpture of their walls is quite 
unlike that found in tracheides in general, and entirely resembles that 
observed as characteristic of vessels in the Magnoliaceae and other families. 
The only difference between the structures in question and typical vessels 
is the absence of actual perforations. This, however, is not a serious 
objection. In the Cactaceae and Crassulaceae among the Dicotyledons are 
found vessels which by the loss of their terminal pores have ceased to 
be technically of the character of vessels. An examination of the genus 
Opuntia among the Cactaceae by Miss Bliss, working in this laboratory, has 
made it clear that what are occluded elements of a vessel-like nature in the 
later wood are patent vessels in the region of the pith. In certain of the 
Magnoliaceae, where the vessels have not only scalariform perforations but 
also scalariform pits on their lateral walls, we have merely to imagine 
1 Holden, Ruth: Ray Tracheides in the Coniferales. Bot. Gaz., vol. lv, No. 1, Jan. 1913, 
Pis. I and II. 
2 Jeffrey, E. C. : Traumatic Ray Tracheides in Cunninghamia sinensis. Annals of Botany, 
vol. xxii, 1908, pp. 593-602, PI. XXXI. 
