50 WOODY PLANTS OF MASSACHUSETTS. 
trunk. One of these whorls is formed each year, from the row 
of buds which encircle that of the leading shoot, thus furnishing 
an easy mode of ascertaining the age of young trees. Where 
they grow together in thick woods, as occurs every where in 
our primeval forests, the lower whorls of branches speedily 
decay, from the absence of light and air, leaving a smooth 
trunk, rising with a beautiful shaft and scarcely perceptible 
taper, without a branch, to the height of 60 or even 100 or more 
feet. In the same manner grow the spruces and firs, and so the 
white pines in Maine still grow. Most of these forests, of the 
larger trees, have disappeared from Massachusetts, though a 
few are still to be found. In the cedar swamps, the straight 
stems are often found so near together, that such swamps can 
with great difficulty be penetrated. 
The disposition and direction of the branches present striking 
differences in the different species, giving them each a peculiar- 
ity of aspect by which they can easily be distinguished at a 
distance. The regular horizontal stages of the white pine, the 
round, tufted masses of the pitch pine, the fan-like branches o 
the arbor vitee, the formal pyramid of the spruce, the graceful 
cone of the fir, the fantastic and irregular raggedness of the red 
cedar, the spiry grace of the white cedar, and the softness and 
delicate outline of the hemlock, must have struck every ob- 
server. When growing naturally in the forest, the branches are 
always small; but when a tree stands by itself, the branches 
often grow large, and are numerous and permanent; and when 
the leading shoot is destroyed, the upper branches, particularly 
in the white and pitch pines, attain a great size. The bark of 
these trees, while young, is thin, and in most cases smooth. 
In the pitch and red pines and in the spruce, it is always rough. 
On the fir, it remains always thin and comparatively smooth, 
and full of cavities or crypts containing the balsam. In most 
of the true pines, it becomes, on old trees, very thick, rugged 
and deeply cleft. In the hemlock, and larch, and in some of 
the pines, it is charged with tannin. 
The wood is disposed in concentric circular layers. Tyhe 
fibres are parallel and not closely arranged, but have consider- 
able strength and elasticity. 'The wood differs physiologically 
