66 THE ROYAL SOCIETY OF CANADA 
wood, and second, to afford a place for the storage of reserve food sub- 
stances. 
It is in these functions of the vertical strands of cells that the rules 
governing the appearance and position of the so-called resin canals of 
the Coniferæ, in whatever forms they occur, will be found, and not in the 
need of resin on the part of the plant, as is usually considered to be the 
case as shown in the treatment of the traumatic appearance of resin ducts. 
Thus, in a form where there is an abundant supply of food formed 
at the very beginning of the year, as is shown by the development of 
the vascular cylinder, e. g., in our specimens of Pinus banksiana, these 
aggregates will appear in a ring in the region of the wood first laid down. 
Where, however, the manufacture of a large amount of food does not 
occur till a later period, the canal tissue will appear later, as is evident 
in our material of Pinus strobus. Again, the same species may show 
great variations in the position and development of the canal tissue in 
the vascular cylinder, according to its habitat and the special conditions 
of growth which it is subject to. This is especially well illustrated by a 
comparison of our specimens of Pinus banksiana with the description 
of this form in the Manual of North American Gymnosperms by Dr. 
Penhallow (25, 321). Whatever differences are exhibited are due to 
normal causes, as our specimens were in no way subject to disease or 
wounding. 
Again, in forms where these cell aggregates are laid down at the 
close of the growth season, it is most probable that the greatest amount 
of food in these forms is present at this period, the parenchyma cells 
serving as a storehouse for any food which is not used up, and which 
can not be accommodated in the cells of the medullary rays. 
The conduction of foodstuffs by the elements of the vertical aggre- 
gations of parenchyma would of itself be favorable to the initiation of a 
vertical cleft or passage. The amount of food available to the growing 
tracheids surrounding the parenchyma cells would obviously be larger 
than that of the tracheids not so situated and these would, therefore, 
undergo greater extension. This rapid extension would be enough to 
rupture the delicate cellulose walls of the parenchyma group at some 
point or points and thus afford a schizogenous passage. That the tra- 
cheids adjacent to the parenchyma elements do undergo more vigorous 
growth than the other tracheids can be seen more or less clearly in all 
the forms examined by the writer, but is shown particularly well in 
some of the forms and may even be a character of diagnostic value. 
Thus Penhallow (25, 314), in describing a cross section of Pinus reflexa, 
states that the “Resin passages are numerous and large, chiefly in or 
near the summer wood, the epithelium composed of large and thin- 
