163] ENGELMANN—REVISION OF THE GENUS PINUS, ETC. 3 
about 20 years, in Cata/fa not more than 2 or 3 years. The 
thickness of the sapwood in pines is usually 2-4 inches, and rarely 
under 1 inch; in P. ponderosa I have found it sometimes even 
Io inches. 
The wood cells and especially those more compact ones of the 
late summer growth, the outer part of the layers, are often 
strongly impregnated with resin and thereby darker colored, yel- 
lowish or brown, and become in thin sections semi-transparent ; 
_ this is much more the case in those of the section Pinaster than 
of Strobus. The former have mostly heavier and harder wood 
than the latter, though we find exceptions, such as P. contorta, 
which has soft wood similar to that of the white pine or spruce. 
Spirally marked cells, such as abound in. Pseudotsuga and in 
Taxus, have not been found in the pines. 
The LEAVES, in the wider sense, are of seven different forms: 
the cotyledonous or seed-leaves, the primary leaves, the ordinary 
bracts, the secondary leaves, the bracts constituting the sheath 
of these, the bracts forming the involucrum of the male flowers, 
and the bracts supporting the carpellary scale. 
The CoTYLEDONOUS LEAVES form a whorl of 4 to 18 in num- 
ber, are triangular, flat on the back, keeled above, higher than 
broad and mostly entire; in P. Strodus I find the keel slightly. 
spinulose -dentate. Stomata are found only on the inner and 
upper sides, as is the case in the cotyledonous leaves of most 
conifers; those of Scéadopitys are, as far as I know, the only 
ones that have stomata merely on the under and none on the 
upper side. ; . 
The PRIMARY LEAVES succeed the cotyledons on the main 
axis ; in some species (P. zxops, P. rigida, P. Canariensis, etc.) 
they are also found on the sprouts. They are always subulate 
from a broader base, flat, keeled on both surfaces, always serru- 
late, even in those species whose secondary leaves are entire (P. 
edulis), with stomata in rows on both surfaces, more on the lower 
than on the upper face. 
The primary leaves not rarely produce in their axils buds with 
secondary leaves, but they are most generally reduced to BRACTs 
(Hochéblaetter) before their axils become productive. These 
bracts are triangular-lanceolate, membranaceous or coriaceous, 
