[KrrscH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 65 
tions of Kny (17) that, wherever a medullary ray borders on the thin- 
walled cells which directly bound a resin-passage, the tracheidal ele- 
ments of the ray are replaced by living ones. This feature, according 
to both authors ,entails an interruption in the tracheidal conduction of 
water in the medullary ray, which, however, they do not attempt to 
explain. According to our view, on the contrary, this apparent inter- 
ruption is a feature which is to be expected, owing to the primary 
relations between the elements of the medullary ray and those of the 
vertical parenchyma aggregates. The primary function of the medul- 
lary ray is the conduction of foodstuffs from the phloem to the growing 
elements of the wood, and hence any secondary functions, such as the 
radial conduction of water, would be subservient to the conditions 
imposed in the maintenance of the first named activities. 
This, however, brings us to a consideration of the functions of the 
vertical parenchyma in the Conifer, whether aggregated in masses 
which afford the formation of the so-called resin-passages, or whether 
they are merely scattered among the tracheids in rows of single cells. 
If, as Strasburger states, the resin formation in the medullary rays is 
only the last function of the living cells, there is no reason, as far as our 
own observations have shown, to assign only this function to the verti- 
cal parenchyma cells, since they are capable of, and do perform more 
primary functions. The resin produced by them is merely an excretion 
resulting from their metabolic activity. If, on the whole, they exhibit 
somewhat larger amounts of resinous contents than the average medul- 
lary ray cell, it is probably due to the fact that they are normally 
produced either during periods of great activity, or when there is a large 
amount of reserve food to be taken care of, and conditions are thus 
favorable for the production of an abundance of resin. 
It must be borne in mind, however, that only the vertical par- 
enchyma surrounding the resin-passages of the wood and secondary 
cortex are under discussion, the bounding layers of the canals in the 
primary cortex not having been examined in detail. Whether the 
latter ducts follow the same rules as regards their origin and function 
as the ones in question will be left for future treatment. 
The primary function of the vertical-parenchyma, taking into con- 
sideration the various facts brought out above, must be regarded as 
identical with that of the medullary ray cells. Now, the medullary 
rays, besides serving for the radial conduction of foodstuffs from the 
phloem to the cambium and the growing tracheids, also serve as the 
place for the accumulation of reserve food. Hence, it may be stated, 
that the primary function of the vertical parenchyma, in whatever 
manner it occurs in the Coniferæ, is to aid the medullary rays, first, in 
distributing the organized food rapidly and uniformly to the growing 
Sec RIVE LOIS: 
