1918] BLISS—TAXINEAE 55 
Those who hold that the Taxineae represent a modern group 
in the evolution of the conifers interpret the facts already stated 
in PENHALLOW’S argument as evidence of an entirely different 
progression. Starting with the genera in which the resin canal 
is highly specialized and resin cells wholly lacking, as in Pinus, they 
trace a series in which there is a gradual reduction of the resin 
canal, to aggregations of resin cells as in Taxodium, to scattered 
resin cells as in Sequoia and Podocarpus, to entire absence of resin 
cells as in Taxus. 
As evidence of the fact that resin canals represent a primitive 
condition in the conifers, JEFFREY’s work on the genus Sequoia may 
be cited. If the presence of resin canals were evidence of modern 
development, we should expect to find them in the mature and 
more progressive parts of the plant, but in Sequoia gigantea JEFFREY 
(5) found the resin canals only in the first annual ring in the stem, 
in the ovulate strobilus, and in the leaf traces of very vigorous 
leaves of adult trees. In Sequoia sempervirens the resin canals 
were wholly lacking in these regions, but in injured stems and roots 
of both S. gigantea and S. sempervirens resin canals were present. 
In the case of Sequoia, then, the presence of resin canals represents a 
primitive condition in the conifers, retained only in the more con- 
servative regions of the plant in S. gigantea, and wholly absent in 
S. sempervirens. A reversion to the ancestral condition in both 
species may be induced by injury. 
According to this later view of the position of the Taxineae as 
contrasted with that held by PENHALLOW, we have a series of 
genera starting with Pinus as a representative of the most primitive 
group in which resin canals are normally present, proceeding 
through Seguoia as a type of a group in which resin canals are not 
normally present in the vegetative axis, until we come to Podocarpus, 
a representative of a group in which resin canals are never present. 
In this connection it is important to note that in those groups in 
which resin canals are normally absent the secretion of resin is 
carried on by resin parenchyma cells. These resin cells are char- 
acteristic of the Taxodineae, Cupressineae, and Podocarpineae. 
We should expect as the logical outcome of this gradual reduction 
and simplification of resin secreting structures the final passing out 
