BALSAM FIE. 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 their 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. Tiie 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 



