REVISION OF THE GENUS PINUS. 361 
P. ponderosa (at least in California) comes very near it; these two are probably the largest pines 
known. 
The AGE of pines varies between 15 to 25 years (P. fideroatlach and perhaps P. montana), 300 
years (P. mitis, P. ponderosa, P. Balfowriana), and 500 to 600 years (observed in P. monticola and 
P, Lambertiana). 
The BARK in some species is thin, only a few lines thick, flaky and detached in scales (P. contorta, 
P. resinosa) ; in others (e. g. P. ponderosa) it is several inches thick, persistent, rough, and deeply 
cracked. It is gray in some species, e. g. in the nut-pines, but most commonly of a brown red or 
cinnamon color, or sometimes deeper brown ; in P. Australis and P. LHiliottii, especially in the latter, 
it is laminated, the external layers peeling off in thin plates. 
The woop grows rapidly, especially oe the — (often the first 50) years of their age, so that 
annual rings are sometimes 2 or 3 lines thick; glabra I have seen them even 6, in P. insignis 
5 and in P. rigida var. serotina 4 lines thiok j ; in old age or in the short seasons of high altitudes 
the wood grows so slowly that sometimes ten annual rings make not more than the thickness of one 
ine. 
The sapwood is always white, and it takes many years before it turns into perfect or heart-wood : 
in P. ponderosa, Lambertiana, and mitis sometimes 100 or even 150 years; in others, e. g. P. flexilis 
and Sabiniana not more than 20 or 30 years; but the majority of pines which I have examined may 
require 50 or 60 years to mature their heartwood. In many other trees this process takes 
about 20 or 30 years, in most oaks on an average about 20 years, in Catalpa not more than [163] 
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 10 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, yellowish 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 number, are triangular, flat on the back, 
"keeled above, higher than broad and mostly entire ; in P. Strobus 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 Sciadopitys 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. inops, 
P. rigida, P. Canariensis, ete.) they are also found on the sprouts. They are always subulate from 
a broader base, flat, keeled on both surfaces, always serrulate, even in those species whose secondary 
leaves are entire (P. edulis), with stomata in rows on both eprascous 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 (Hochblaetter) before their axils become productive. These 
bracts are triangular-lanceolate, membranaceous or coriaceous, entire or mostly fringed on the [164] 
edges, more or less persistent or mostly deciduous, sometimes articulated above their base. 
The SECONDARY LEAVES constitute the ~~ of the tree: they are borne on an undeveloped 
