Cretaceous Pine Leaves. 
399 
species approximated also to the modern type of Pinus in having a bundle, 
not separated actually into two as is frequent in the modern species, 
but split by the ingrowth of the inner thick-walled sheath. 
For the moment, however, we find facts more attractive than theories, 
and will describe another species of leaf from this horizon. 
Pinus yezoensis, sp. nov. 
This species resembles much more closely the living Pinus than do any 
of those described by Jeffrey. As is seen in Phot. 3, PI. XXVII, it is oval in 
section, with no straight side, and has a very well marked endodermis round 
the bundle and comparatively small transfusion zone. The leaf is about 
i-i mm. in diameter. 
The epidermis consists of small, rather roundish cells, about o-oi mm. 
in diameter. The stomates are of the usual Gymnosperm type and are few 
in number. 
The hypodermal sclerenchyma consists of a zone, two or three cells deep, 
of small cells with but slightly thickened walls. 
The assimilating tissue of the leaf is well preserved, and consists of 
large cells (0-08 mm. in diam.) entirely like those of modern Pines, with 
curved walls folded into ridges projecting into the cell cavity (a in Phot. 4, 
PI. XXVII, and Fig. 2, PI. XXVIII). 
The resin-canals are two in number, placed laterally and towards the 
upper side of the leaf. They lie immediately under the hypoderm ; see g, 
Phot. 5, PI. XXVII. Each canal is about 0-035 ' m diameter, and is sur¬ 
rounded by a dozen epithelial cells which are roundish in outline, and very 
well petrified; see ep, Phot. 5, PI. XXVII. 
The vascular tissue is surrounded by a large, well defined endodermis. 
This is seen clearly in Phots. 3 and 4, PI. XXVII, and Fig. 2, PL XXVIII, 
en, and is entirely similar to the endodermis in the living Pines. 
The individual cells are large and oval, about 0-06 in diameter, and 
their radial walls fit together and appear to have been slightly thickened. 
In view of Jeffrey’s (’ 08 , p. 216) statements about the American 
Cretaceous Pines, the exceedingly clear endodermis and the infolded walls 
of the mesophyll are both noteworthy features of this species. 
A few sclerized cells occur within the endodermis, and these may 
possibly represent the remains of an inner thick-walled sheath such as was 
noted in Prepinus. There are one or two cells at the sides of the bundle 
which may have been transfusion cells, but the bulk of the tissue within the 
endodermis consists of the vascular tissues proper. 
The xylem is arranged in radial series, a dozen or more rows of 
tracheides separated very widely by large medullary ray cells (see Phot. 4, 
PI. XXVII, and Fig. 2, PI. XXVIII, m and x ). The xylem appears to 
have been entirely centrifugal. 
