SO THE ROYAL SOCIETY OF CANADA 
Lastly, he says, “If the general principles of comparative anatomy 
enunciated at the beginning of this discussion are correctly formulated, 
the Abietinæ have come from a stock characterized by the presence in 
both fundamental and fibrovascular tissues of resin ducts which form 
a continuous system of horizontal and vertical canals, such as are found 
in the living Pineæ. . . . . The ancestral forms provided with a com- 
prehensive and freely anastomosing system of resin canals . . . .were 
thus safeguarded against infection in case of injury, but at a great cost 
both in the large supply of resinous secretions necessary to supply 
the needs of this extensive system, and in the large quantity expended 
in sterilizing a wound . . . . . Gradually the more economical ten- 
dency arose of forming resin passages in the case of need only 
the place of this system is taken by the much less costly expedient of 
resin cells and by traumatic ducts which are formed in case of need 
only.” 
Now, if, by the obliteration of the resin ducts and their replacement 
by resin cells, the ducts being formed only when necessary, an economy 
is provided in the growth of the plant, it would naturally be expected 
that there would be an increase in the amount of other tissue formed. 
Thus, it would be only natural that in trees where these structures 
normally occur, those rings which possess the fewest and least developed 
canals would be most vigorous, those possessing the largest number of 
ducts being the weakest. The exact opposite is, however, the case, and 
it is found that where, e. g., in Pinus, the canals are entirely absent or 
only scattered, that the growth of the ring has been reduced to a mini- 
mum, while the most vigorous annual rings are frequently characterized 
by several zones of canals. 
Moreover, the formation of canals only on wounding would be a 
rather false economy on the part of the plant, for, as has been shown 
above, only that resin already present is of immediate use to the plant 
when injured. 
From the above consideration of Jeffrey’s observations and con- 
clusions it can be seen that his reversion theory does not really clear 
anything up, all his data being capable of a more rational explanation 
by means of the conclusions based on our own observations. It is thus 
seen that the traumatic appearance of the so-called resin canals is due 
to the same general causes as those which call forth the normal forma- 
tion of these structures in other species. Far also from being a reversion 
to ancestral features, it shows the mode of development of these struc- 
tures in the progressive differentiation of tissues. The Conifers, as a 
whole, probably came from an ancestor or ancestors of the same charac- 
ter as the ancestor of the woody Dicotyledons, but in the case of the 
latter there was an abundance of wood parenchyma present, both in the 
