102 FAMILIAR TREES 
The Hemlock Spruces (fsuga) have but one central 
resin-canal in the leaf, the true Spruces (Picea) have 
-one or two lateral ones, and the Douglas Fir (Pseudo- 
-tsuga), like the Silver Fir (Abies), has always two 
lateral ones. The leaves of the Douglas Fir are 
arranged singly and spirally as in both Spruces and 
Firs, but though twisted so as to form a two-sided 
spray, they do not he as flat in two rows as do those 
of the Silver Fir, but are rather in three or four 
‘rows. They are of a bright shining green above, and 
remain on for six or seven years. Three-quarters of 
an inch to an inch and a quarter long, they are flat, 
narrowly linear in outline, bending slightly upwards 
at the apex, and varying considerably in the sharp- 
ness or bluntness of that extremity. The stomata 
-are confined to two silvery lines, which are fainter 
than those of the Silver Firs. In section the leaf is 
elliptical, without the thinner areas on either side 
of the midrib characteristic of Abies and Tsuga, or 
the four-sidedness of Picea. The hypoderm varies, 
but is generally only slightly developed; there is 
a large-celled mesophyll and a single undivided 
vascular bundle, much as in Picea. 
The staminate flowers are mostly on the under 
side of the twigs of the preceding year, forming 
axillary egg-shaped masses. The pollen-grains have 
not the air-bladders that occur in the Pines. 
The tree generally bears cones from about its 
twenty-fifth year. These very distinctive features are 
borne at the apex of the twig, hanging downwards, 
first appearing in May, ripening in their first year, 
and falling off whole. They are egg-shaped, from two 
