ON THE PINES OF AUSTRALIA. 169 
medullary rays are rather obliterated by the resin contents. 
However, the pictures define clearly that the outer cells 
of the rays are of identical structure to the inner ones and 
that the whole group may be classed as parenchymatous. 
This is a distinct difference of form or structure of the cells 
of medullary rays from some living non-Australian Pines. 
In the same figure it will be noticed that the narrow 
lumina of the autumnal wood are towards the right of the 
picture. 
The numerous bordered pits are in single rows on the 
medullary walls of the tracheids, and are well brought out 
in both plates. The simple pits of the medullary rays are 
distinctly seen at the top right hand corner and the bottom 
of Fig. 20. The diameters of the bordered pits varies 
according to that of the tracheids, and the presence of 
resin in the tracheids is marked by the darkened content. 
Fig. 20 has only one resin cavity which is low down in the 
right hand corner, and Fig. 21 has three on the right hand 
centre of the field of observation, being the vertical views 
of the resin cells of Figs. 17 and 18. 
Medullary Rays.—In addition to what has been stated 
under Fig. 20 it may be further remarked that these organs 
present novel features when compared with those of 
Angiosperms. In the radial and tangential sections they 
are found to consist entirely of narrow parenchymatous 
cells circular in form when viewed tangentially in the 
wood. Hach ray is composed of a varying number of cells 
arranged in horizontal parallel strata only a single cell in 
breadth. Most of the outer and inner cells are filled with 
resin similar to the vertical cells, the radial walls being 
marked by the presence of simple pits, and cells void of 
resin are the exception. In Figs. 22 and 23 they are shown 
radially in situ in the wood substance, the varying length 
evidently due to the plane of cutting, the vertical diameter 
being almost equal in each case. 
