[KIRSCH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 67 
walled, very resinous cells; when in the summer wood the resin passage 
is central to a large tract of thin-walled tracheids.”’ This illustrates 
our point perfectly. 
The vertical parenchyma of the Coniferæ would thus perform the 
same general functions as those of the Dicotyledons, and would be a 
manifestation of the same tendency towards a higher organization. 
Schulz (31, 339), dealing with the medullary rays of the Dicotyledons, 
says “The wood parenchyma and the medullary ray tissue stand in 
intimate relation with the vessels, and with these constitute the channel 
for the conduction of organic fluids.” The same may certainly be said 
of the wood parenchyma and medullary ray cells of the Conifer, for 
they are elements of the same general nature as the above. 
The medullary rays of the Coniferæ are always accompanied or 
traversed by intercellular spaces which communicate with the inter- 
cellular spaces between the living elements of the wood and bast (32, 
140). These intercellular spaces filled with air begin in the periphery 
of the stem and penetrate the cambium. All the living elements are 
thus kept in communication with the atmosphere, and the necessary 
interchange of gases is thus insured. The intercellular passages in the 
ageregates of vertical parenchyma are merely a part of this aerating 
system, resin appearing in them owing to the efforts of the active epi- 
thelial cells to get rid of the excreta and thus voiding it in the most 
available place. 
That the function of resin production is not a primary feature of 
the passage is also seen in the fact that they are far from forming a 
continuous system even in those forms where they occur most abund- 
antly. Moreover, in some forms they are altogether isolated, as is the 
case in the species where vertical canals only occur, the connecting 
horizontal ones being altogether absent. Strasburger (33, 2) states, 
“Tn spite of these unions (1. e., the unions of the vertical and horizontal 
canals), and the lateral anastomoses, the resin canals are far from 
forming a continuous system in the inside of the stem; the parenchyma 
cells surrounding them, on the other hand, through junction with the 
medullary rays, form a part of the great parenchymatous system (Hin- 
heit), which draws its nourishment from the starch conducting phloem.” 
The conclusion to be drawn from this passage is obvious. 
Mobius (22, 262), in discussing the nature of the resin ducts, asserts 
that, in many cases, especially where the resin passages are local and 
not part of an extensive canal system, they serve only to take up any 
excreta that the plant wishes to get rid of. In passages which are in 
connection through whole organs, or even through whole plants, it must 
be presumed, on the contrary, that a secretion laid down at one point 
is transmitted to another, so long as no interruption in the continuity 
