1897] NORMAL AND DISEASED ORGANS OF ABIES BALSAMEA 331 
found in the primary cortex of the older branches. They 
increase in size by the distention of their cell walls ; consequently 
the larger mucilage cells are thinner walled. 
The resin canals are always lined with one layer of epithelial 
cells. Surrounding this layer there are always present one or 
two layers of collenchymatic strengthening cells. Noresin canals 
are formed after the first year, and during the first year only in 
the meristem tissue of the developing shoot, where they reach 
their definite size as soon as the tissue differentiation has taken 
place. After the resin canal has reached its definite size, the 
epithelial lining probably loses its resin secreting function; but 
its cells still remain thin walled and are able to divide, like 
ordinary parenchyma cells. 
It is evident that with the increase in the diameter of the 
main axis and the peripheral growth of the bark, disturbances 
must occur in the resin canals of the primary cortex. As has 
already been stated, the primary cortex of A. dalsamea remains 
alive, and is not thrown off by the formation of cork scales 
before the tree stems are from 50 to 100 years old. With the 
increase of the peripheral growth of the tree trunk, however, the 
resin canals are often disturbed by the cork cambium, which at 
places penetrates deeper into the primary cortex. Mayr* has 
demonstrated that as soon as a resin canal comes in contact with 
the cork cambium, the canal is filled up by the ingrowing of its 
epithelial cells, forming the so-called tyloses. Inthe develop- 
ment of each internode, a new system of resin canals is formed 
in the primary cortex, so that the canals of one internode do not 
connect with the canals of the adjoining internodes. The canals 
_ are always filled with an oleo-resin, so long as the formation of 
cork has created no disturbance in the turgescence by the loss 
of water from the cells surrounding the resin canals. The main 
resin canals are vertical and traverse the whole length of the 
internode. In older stems they are not always vertical, since the 
peripheral growth of the bark and main axis is not always 
_ “Mayr, H.: Harz der Nadelhélzer; ; seine Entstehung, haem Bedeutung 
gears 21.1 1894. 
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