ee ———eeEeEeeEeOOoO7 
From the characteristics above mentioned the following synoptical 
arrangement of the genus has been arranged. 
*Ducts medial. 
7+Strengthening cells absent or few in number. 
1. Abies balsamea (L.) Mill. Strengthening cells few in number or en- 
tirely absent, thin walled. 
7yStrengthening cells always present in considerable numbers. 
2. Abies Fraseri (Pursh.) Lindl. Strengthening cells in a continuous 
layer within the epidermis, sometimes doubling at the angles, especially 
the dorsal angles. Cells thin walled.. 
3. Abies subalpina, Engelmann. Strengthening cells mostly in the an- 
gles; in a single layer in the lateral angles and a double or triple row in 
dorsal angle, also occurring in groups between the angles. 
**Ducts peripheral. 
7Strengthening cells few in number, occurring singly or in groups. 
4. Abies grandis, Lindley. Strengthening cells occurring singly or in 
groups of from two to five, thick walled, sometimes occur within bundle 
sheath. 
77Strengthening cells abundant in angles of the leaf in single or double 
cows. 
5. Abies magnifica, Murray. Strengthening cells thick walled. The two 
vascular bundles merged into one. 
6. Abies concolor, Lindley and Gordon. Strengthening cells very thick 
walled, some present within the bundle sheath. 
The structure of the leaf of the Picea is about the same as that of the 
Abies. The leaf, however, is of a different shape. In the cross section the 
Abies show a lateral axis very much longer than the dorsi-ventral axis. 
In the Picea the two axes are about equal. There are also other charac- 
teristic differences. The leaf, as in the Abies, is divided into cortical, 
mesophyll and fibro-vascular regions. 
The cortical region. The epidermis is composed of thick-walled cells 
as in the Abies. The strengthening cells are arranged about the entire 
leaf, and like the epidermis, this layer is interrupted only by the stomata. 
The stomata here are also arranged in rows along the side of the leaf. 
Between the openings of the stomata the strengthening cells are much 
thinner walled than in the remainder of the leaf. 
The mesophyll region is composed of wavy-margined, chlorophyll-bear- 
