[KIRSCH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 55 
In the wood there are in the normal condition only tracheids 
separated by medullary rays of the same nature as in the bast. When 
diseased, however, the shoots present the following modifications. The 
annual ring is much thicker, often being two or three times thicker than 
in a like region of an unaffected twig. The autumn wood is neverthe- 
less much less, the tracheids in the region of autumnal growth exhibiting 
much the same characters as the tracheids of the spring wood. But it 
is in the medullary rays of the wood that the greatest changes appear 
(18, 332). Their number, distribution, breadth and height are the 
same as in the secondary cortex of diseased trees. The rays are higher, 
closer together, composed of broader elements, and frequently two- 
seriate. 
Lamarliere says that this great multiplication of the ray elements 
is due to an effort on the part of the plant to provide more food for the 
fungus, since the ray elements besides facilitating conduction in a 
radial direction also act as storehouses for reserve food. He thus evi- 
dently takes this to be a case of symbiotism, which is rather unlikely, 
and it is certainly allowable to state that this is only an example of the 
reaction of the woody tissues in the Coniferæ in the presence of a super- 
abundance of food. The question regarding the nature of the reaction 
of the vascular elements under pathological conditions will however 
be discussed more fully at the conclusion of this paper and so we will 
return to the discussion of the points at issue. 
The origin of vertical strands of parenchyma from the elements 
of the medullary ray, is not limited only to those forms in which definite 
resin canals appear, as can be seen from Fig. 9. This drawing is taken 
from a radial section of Cupressus goveniana, and shows the origin of 
some of the cells of a vertical strand from a medullary ray. This strand 
extended for a considerable distance and probably represents a tendency 
to the formation of resin canals, as recorded by Penhallow (25, 236) for 
Cupressus arizonica. In many other cases parenchyma cells were seen 
to arise from medullary ray elements in forms which normally possessed | 
no aggregates of such a nature and in sections which were not at all 
favorable for the determination of the origin of the structures in ques- 
tion, since they were obtained from old wood. 
Figs. 10, 11, and 12 illustrate the character of the parenchyma 
aggregates as they appear in cross-section in the cambial region. Fig. 
10 is taken from a vigorous second year shoot of Pinus strobus which 
was still forming spring wood when cut, and shows the appearance of 
the parenchyma cells in the cambial region. Two rays are seen here, 
the central one being responsible for most of the parenchyma cells, the 
ray on the left having given off several in addition. The ray on the right 
of the group (not shown in the figure) had no parenchymatous cells in 
