168 R. T. BAKER AND H. G. SMITH. 
any of the tracheids, this is an unusual occurrence, and it: 
simply shows that it is possible to obtain a section without 
resin cavities. The line of smaller or closely packed cells 
marks the autumnal growth and the point of transition 
from that season’s wood structure to that of spring. 
Under a higher magnification ( x 80), as in Figs. 17 and 18, 
a rather more uniform size of cell obtains, for although the 
tracheids are of varying diameters, yet the walls may be 
said to be of a fairly uniform thickness ; in Fig. 17 the black 
lines running from top to bottom are the parenchymatous 
cells of the medullary rays filled with resin—the ‘* end-on 
view ”’ of which is shown in Figs. 25 and 26. In 17 and 18 
are more plainly seen the autumnal tracheids with their 
restricted growth, and which form a darker line across the 
lower portion of the plate; these vessels are slightly 
enlarged in Fig. 18. The gradual diminution in size of the 
tracheids during this period is well seen, as also is the sudden 
change to enlarged vessels of spring period. 
In Fig. 18 there is a portion of a single circle of smaller 
tracheids, four or five cells distinct from the well defined 
autumnal ones, and which evidently indicates a cold snap. 
The resin cavities are plainly shown, but no resinous 
medullary rays are visible. 
Fig. 19 is portion of Fig. 17 under a 210 magnification. 
The cells in the same row are of almost equal diameters, 
and on the lower radial walls of the fifth row from the top, 
bordered pitsin section can just be seen, and the torusis also 
discernible. It will be noticed in several instances, por- 
tions of the inner cell walls are detached and protrude 
into the cell cavity. Whether this is natural or accidental 
in the cutting we could not decide. It hardly appears to 
be a case of tylosis. 
Fig. 20 is an 80 magnification of a radial section of timber. 
The general character of the parenchyma cells of the 
