52 THE ROYAL SOCIETY OF CANADA 
of food present, but by the stimulus of the tensions established by the 
rapidly elongating tissues surrounding them. That these tensions are 
also sufficient to account for the presence of a more or less prominent 
intercellular space between the cells which are last formed, and thus 
for the lumen of the so-called resin canal, will be shown further on. 
Fig. 7 shows a fusiform ray containing a horizontal passage, and 
ending in a cyst in the phloem region, and represents a more advanced 
stage than Fig. 6. In the xylem region, the same ray terminated in a 
vertical strand of cells containing an intercellular passage, this feature 
being dealt with fully below. Accompanying the division of the central 
cells of the medullary ray in the sections examined, and in Pinus, Picea, 
Larix, and Pseudotsuga generally, is the appearance illustrated in Fig. 
8, which shows that in periods of very vigorous growth accompanied 
by an abundance of food, the elements of the medullary rays in the 
wood are able to keep pace with the rapid elongation of the tracheids 
in still another manner. This drawing is taken from a radial section 
of Pinus banksiana as described in lot two, and shows the region from 
the phloem to the protoxylem. Two rays are seen proceeding from 
the phloem to the xylem, and in the latter region they are seen to 
become continuous with a vertical strand of parenchyma cells which 
extended for a considerable distance in a longitudinal direction. 
This, however, brings us to the consideration of our view regarding 
the origin of the so-called resin canals of the Conifers, in particular, 
and of the wood parenchyma strands in general. As was shown above, 
the ray elements, when first laid down, are isodiametric, or even verti- 
cally elongated, and even after growth has proceeded for a time those 
ray elements which possess more freedom of growth, such as the mar- 
ginal cells, still exhibit a definite tendency towards growth in a vertical 
direction. Now, if during the cambial growth of the ray a large amount 
of food is presented to the cells, and if the specific characters of the 
plant are such as to allow the vertical extension of the ray eells, the 
following would ensue:—Since the rays proceed from the bast to the 
wood and bring food to the growing elements of the xylem from the sieve 
tubes of the phloem, the forming cells of the ray are the first elements 
to which the elaborated food becomes available. When there is only a 
limited amount of foodstuff available, the ray elements cannot obtain 
all that they are capable of using up in rapid growth and division, a 
certain amount of the elaborated sap being bound to diffuse into the 
adjacent formative tracheids owing to the presence of the simple pits 
on the connecting walls, and also owing to physical conditions such as 
osmosis present in the growing tissues. When, on the contrary, a 
superabundance of food is available, the ray elements can avail them- 
selves of as much as they are capable of using up in their growth and 
