48 THE ROYAL SOCIETY OF CANADA 
(a) Pinus Strobus.—Sections at the tip showed the vascular 
bundles to be quite separate and no interfascicular cambium present. 
Protoxylem elements were present but no secondary xylem or only 
a few scattering ones in a formative state. The pith was complete. 
At the base, the vascular cylinder was seen to be complete, the proto- 
xylem and several rows of formative secondary xylem elements standing 
out clearly. However, there was still no appearance of any resin 
canals, such as were to be seen in Pinus banksiana of the former week. 
The pith was entire. 
(b) Pinus Banksiana.—At the tip the vascular tissue presented a 
closed cylinder, a ring of resin canals being present in the region of the 
protoxylem, a second ring of canals making its appearance in the form- 
ing wood of the larger shoots. The pith exhibited the same lacunar 
character as in the shoots of the first lot, but several modifications were 
noticed. In some cases the pith was suspended in the centre of the 
vascular cylinder by a few delicate rows of cells of a trabecular character, 
which connected it with the cylinder, and thus large lacunæ between 
it and the cylinder in addition to the smaller ones present between its 
constituent cells were present. In other cases, again, the pith was in 
contact with the vascular tissues but showed a large cavity in the 
centre, thus simulating the appearance of a hollow pith. In sections 
from the base the woody tissues exhibited a perfectly closed and com- 
pact cylinder with as many as 26 rows of xylem cells, whilst sections 
of the same character from the shoots of Pinus strobus rarely exhibited 
as many as fifteen rows. The resin canals were fully developed and 
numerous, being disposed in one or two rings around the cylinder. The 
pith was almost entire and consisted of two kinds of cells, viz., small 
cells containing a large amount of starch and other reserve foods, and 
large bladder-like cells fairly clear of contents, although frequently 
exhibiting nuclei. Again, whilst the small cells were rather thick- 
walled, the walls of the large cells were very thin. In some of the 
sections obtained from the portion of the shoots between the apex and 
the base, the large cells could be seen to originate from the small cells 
in a thylosal manner and to fill up the lacune of the pith. In this way, 
in conformity with the features mentioned above, some sections showed 
a peripheral layer of large cells and a central portion of small cells, 
whilst others showed just the reverse, still other sections showing the 
large and small cells more or less evenly co-mingled. These thylosal 
cells also possess the power of division, and so, in some of the older 
material, their daughter cells were observed to approach the primary 
pith cells in size. In this case the cells could be easily distinguished 
by the thinness of their walls and by the character of their protoplasmic 
contents. 
