BALSAM FIR. 
23 
The crown of a normal tree is always conical, since the lower branches 
are longer than the upper ones. The main branches are arranged in 
whorls of 4 to 6, with here and there scattered solitary branches 
between. The lower branches of a mature tree are long, slightly 
pendulous, those near the middle of the crown horizontal, and the 
upper short branches ascending. As with white pine, the branches 
readily die off, but remain on the trunk for a long time. The crown, 
therefore, may begin very high up the tree, but the clear length in 
the lumberman's sense is comparatively short. This explains to a 
large extent why balsam-fir lumber has, as a rule, more knots than 
spruce lumber. 
FOLIAGE . 
The needles differ in shape and arrangement, depending upon their 
position on the tree. They are sessile, narrow, linear, notched at 
the apex, and from half an inch in length on the upper branches to 
an inch and a half on the lower ones. On the lower branches, while 
actually spirally arranged, they are twisted so as to form but two 
rows, horizontally spread on each side of the branch. On the upper 
branches they retain then ascending spiral arrangement. They are 
dark green above and silvery white beneath on account of the many 
stomata which are arranged in lines and appear as minute, shiny 
dots, and are especially conspicuous in newly formed leaves. This 
arrangement of both branches and foliage is simply a response of 
the tree to light conditions. The top of a tree normally receives 
light from all sides, and needles and branches, therefore, stand out in 
all directions. At the bottom of a tree in the forest light comes 
mainly from above, hence the branches and needles there are ar- 
ranged in a horizontal plane with their functional surface upward. 
Trees that are suppressed have feathery and spray-like foliage, also 
due to light conditions. 
The foliage of balsam fir persists for from 8 to 13 years, depending 
upon the amount of shade and the thriftiness of the tree. Dense 
shade and rapid growth cause the needles to drop earlier; abundance 
of light and slow growth allow them to remain on the tree for a longer 
time. 
LEAF STRUCTURE. 
The leaf structure of balsam fir, as of the entire genus Abies, is 
very similar to that of the pines. It consists of three parts — the 
outer or cortical part, the chlorophyll-bearing or mesophyll part, and 
the fibro-vascular part. The outer part is composed of an epidermis 
and strengthening cells lying directly beneath. The chlorophyll 
part is composed of parenchyma cells, among which are distributed 
the resin ducts. These ducts either lie directly beneath the epider- 
mis close to the periphery of the leaf surface or else are surrounded 
