[KIRSCH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 47 
various tissues was seen as between the two species, the following 
account showing the most salient features of the first year shoots :— 
(a) Pinus Strobus.—In sections taken from the tip to one-third 
of an inch below the tip, the cambium ring was not yet formed, the 
vascular bundles being separated by broad rays of fundamental tissue. 
The vascular bundles showed a strong development of the phloem, but 
in the xylem region only a few protoxylem elements and no secondary 
xylem appeared. The pith was complete and the cortex possessed two 
rows of canals. Sections obtained at the base of the shoots showed 
that the vascular cylinder was closing up, the cambial ring being almost 
completed by the interfascicular cambium, although some of the 
bundles were still separated by broad rays of parenchymatous tissue 
in the xylem region. The protoxylem elements were very numerous, 
consisting in some of the bundles of several rows of cells and in addi- 
tion to these the secondary xylem was making its appearance. No sign 
of resin canals was observed in the vascular tissue. The pith was com- 
plete and consisted of cells of equal size. 
(b) Pinus Banksiana.—Sections from the tip showed that the vas- 
cular cylinder was beginning to close up, although the interfascicular 
cambium had not appeared between all the bundles. In the individual 
bundles the protoxylem was fully formed and several rows of secondary 
xylem were in a formative state. Moreover, in each bundle two or three 
resin canals were present in the xylem region in the immediate vicinity 
of the protoxylem, one of these canals being represented in Fig. 1. 
The pith was not complete, but was composed of strands of equal- 
sized cells arranged in the form of a network, and thus exhibited a 
lacunar structure. The cortex possessed one row of resin canals, but 
the epidermis and the outer cortex did not yet show their characteristic 
structure as exhibited in more mature parts. The sections taken at 
the base showed the vascular cylinder closed and the canals in the wood 
well developed, some of the sections showing canals formed even in the 
pith. Fig. 2 represents a radial tract of tissue from one of these sections 
extending from the pith to the phloem. Adjacent to the medullary 
ray two canals are seen, one being in the pith, the other in the wood. 
Whilst the section from which this was drawn was 4-8 mm. in diameter, 
some of those which did not show this feature were only 2-5 to 3 mm. 
in diameter, and therefore the pith canal is undoubtedly associated with 
the very vigorous growth of the shoot in which it occurred. The pith 
exhibited large lacunæ, and in several cases large cells were seen to be 
filling up some of the lacune. 
In the second lot, the first year shoots of Pinus strobus were 10 to 
12-2 cm. long and 3 to 4-5 mm. in diameter, whilst those of Pinus 
banksiana were 17-8 to 24-2 em. long and 3-5 to 6 mm. in diameter. 
