68 THE ROYAL SOCIETY OF CANADA 
of the passages occurs. Continuous systems of resin canals, in any of 
the Conifer, are, however, conspicuous by their absence, and, where 
any approach to continuity is observed it is merely a result incidental 
to rapid and vigorous growth and occurs in individual cases only, not 
being characteristic of any species or variety. 
Moreover, in the needles of the Coniferz, the resin canals are rarely 
connected with those of the cortex, except in cases of abnormally vigor- 
ous growth, and hence any resin produced would be ultimately lost to 
the plant, which is certainly not a feature of a true secretion, but which 
is characteristic of waste products. Again, the number of canals 
present in any needle (34, 51) is entirely dependent on the vigor of 
erowth, and in one case Mobius (22, 265) even mentions a species of 
pine, Pinus radiata, which is distinguished by the very delicate character 
of its needles, and in which no resin canals occur. The same holds true 
for the cortex, also, more canals being formed as the vigor of growth 
increases. It can, therefore, be seen that both in the needles and in 
the cortex the formation of the canal is not dependent on the presence 
of any canal mother cell, which by division develops a secretory duct, 
as Mayr asserts (19), but that in all probability it follows the same 
rules as do the canals of the wood, although the origin may be slightly 
different. From the above it is also evident that the resin is not a 
secretion in the true sense of the word, but that it is an excretion due 
to the metabolic activities of the plant, and which, under certain con- 
ditions, may be of use to it. 
It is a general rule that resin when it once appears in a cell in a 
visible form, never leaves that cell again, and in this feature may be 
found the probable use of the excretion to the plant. On the boundary 
between the sap and heartwood, only the central cells of the medullary 
ray are alive, and contain resin drops and isolated starch grains, while 
the cells lying near the margins of the ray are already void of proto- 
plasm and contain resin partly as drops and partly as linings of the wall. 
Moreover, in the heartwood, according to Mayr (19, 283) the resin 
normally appears only as a lining of the medullary ray and wood par- 
enchyma cells, never appearing in the tracheids if these are uninjured. 
It is at this stage that the resin is probably of most use to the plant as 
it prevents the elaborated food from flowing through the medullary 
rays and wood parenchyma into the functionless parts of the plant, 
where it would not only be wasted but would tend to bring on decay. 
This would be admirably arranged for by the resinous linings of the 
parenchyma cells both of the rays and the strands, which would block 
the pits and render the cell wall impermeable to the elaborated sap. 
That the production of a large amount of resin is due to the presence 
of parenchymatous elements in the wood, and not to any special need 
