260 BOTANICAL GAZETTE. [Oct., 
which, in many eases, are thick-walled strengthening cells, either 
scattered about the duct or forming a compact sheath. 
Ill. The fibro-vascular region, A very distinct bundle-sheath 
invests this region, the cells of which are either comparatively 
thin-walled, or with the outer wall excessively thickened. This 
has been a useful character in some of our subdivisions, but is not 
always constant. P. Sabiniana, P. Coulteri, and a few others may 
or may not have the bundle-sheath with thickened outer walls. 
Tn the center of this region occur the fibro-vascular bundles, either 
one or two. This character we have used as one of the best for 
separating the genus into two sections. As has been mentioned, 
Dr. Engelmann considered it of but slight diagnostic importance, 
but we have found no character less likely to fail. In the examina- 
tion of many hundreds of sections but one was different from the 
expectation in this regard. The bundles are always together at 
the base and apex of the leaf, and may be widely separated dur- 
ing the remainder of their course, but even when they are in con- 
tact they can easily be distinguished as two. In the use of the 
terms “ dorsal” and “ ventral”, when speaking of the leaf sur- 
faces, the former is applied to the phloem side, the latter to the 
xylem. Strengthening cells may or may not be found about the 
fibro-vascular bundles, and this is such a constant character as to 
good service in classification. The rest of the fibro-vascu- 
lar region is filled with parenchyma cells and tracheids, neither of 
which are of any diagnostic value. : 
sing the structural characters described the following syn- 
optical arrangement of our pines, including some Mexican species, 
is presented, for the purpose of supplementing other characters, for 
use in the absence of other characters, and to indicate relationships. 
1. Fibro-vascular bundle one: leaves mostly in fives. 
*A thin-walled layer next the epidermis (somewhat thickened in P. mon- 
ticola) : no strengthening cells next the epidermis nor about the ducts: leaves 
always in fives. 
t Stomata on dorsal side of leaf.® 
1. P. albieaulis Engelm. Epidermis mostly very  thick- 
walled: one to three rows of dorsal stomata: two dorsal ducts 
(.050-.070 mm.); often a ventral duct, sometimes one or more 
smaller accessory ones: thin-walled cells about ducts larger than 
those next the epidermis; leaves 2 in. long. 
Along the Coast Range, from California to British Columbia. 
This does not mean that there are no ventral stomata, 
