[KIRSCH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 79 
a longitudinal direction than in the normal shoots. It would be in- 
teresting to find out whether the growth of the shoot, both in traumatic 
cases or in the other forms mentioned by Jeffrey, exhibited an increase 
in length proportional to the greater thickness, as this would elucidate 
the conditions under which horizontal canals may be formed. 
As showing how the formation of resin canals in forms where they 
are generally absent depend altogether on the place of growth and 
individual characters, may be mentioned the case of the cone of Cedrus. 
Jeffrey found no canals present in these, but Radais (26, 250) states 
that “The secondary wood of the axis of the cone of Cedrus deodora 
possesses secretory canals.” In Cedrus libani these were absent, but 
on an examination of the figures given by this author it is obvious that 
C. deodora was of much more vigorous growth, the canals of the cortex 
in C. deodora being several times larger than in C. libani. Thus the 
presence or absence of this structure depends entirely on the vigor of 
growth. In this connection an observation by Strasburger is very 
pertinent, since it shows that the resin cells behave in the same manner 
as the resin canals. In examining branches of Cedrus libani he found 
that not only did different specimens exhibit great differences in the 
number of rows of wood parenchyma present, but even different rings 
of the same branch showed this feature (33, 3). 
Jeffrey’s observations on Tsuga also bring out an interesting point, 
since they show that the position of the traumatic canals in a growth 
ring may be moved forward, if the wound is very severe. This is in 
direct line with our interpretation of these structures, since in the case 
of severe and extensive injury more food would be present near the 
wound than in case of smaller wounds, and hence the formation of con- 
ducting elements would be hastened. 
In the conclusion of his memoir on the Abietine, Jeffrey states that 
one of the principles of comparative anatomy is “that ancestral features 
are apt to linger on in the reproductive axes after they have disappeared 
from the vegetative organs.” But in all the cases mentioned by him 
the structures in question “lingered” only in the female cone, and no 
sign of it was exhibited in the male cone as far as his observations go. 
The occurrence of the ducts in the cones in question, can, however, be 
much better explained than by invoking any canons. 
Moreover, Jeffrey, according to another principle, should have 
found resin canals present in the first annual ring of the seedling, but he 
did not observe any such appearance. He explains this on the ground 
that the tree has been reduced from a more luxuriant ancestry, but 
this does not explain the fact, for if it were a reversionary feature it 
should linger on in this position also. 
