46 
the vails of the smaller cells, parallel to the medullary plates, is due 
to the cross-section of the lenticular markings. 
The walls of each cell are composed of three layers — an inner one, 
quite thin and surrounding the lumen ; then a thick one, and, lastly, a 
thinner one, which is so delicate that between the adjacent cells it ap- 
pears as one wall ; but, in some woods, is known to consist of two dif- 
ferent layers for each cell and is believed to be so in all ; its division can 
be seen in the transverse section of the Tamarack.* 
In the radial section the longitudinally arranged cells are seen with 
their lenticular markings. It is generally stated that in the duramen 
the lamella between the domes of each one of these markings becomes 
broken, so that there is a free communication between the cells ; this is 
not the case : the delicate membrane is pushed over to one side in the di- 
rection of the exit of the sap, and may be found by the highest grade 
of objectives. When it is covered with resinous products the passage of 
heavy fluids is much impeded and this is one of the reasons why, with- 
out special treatment, it is so difficult to secure the penetration of preserv- 
ing fluids in this wood. These cells can be filled with any antiseptic 
(creosote combined with an oil, etc.), but it is a question of time, heat, 
and vacuum. 
The walls of the more open or larger cells are seen to be some dis- 
tance apart; the white space shows their cavities, with the lenticular 
markings appearing in the background as it were, or in this class of 
tracheids in plains parallel to those of the medullary rays. The dark 
upright bands shown in the photomicrograph represent the thick walled 
tracheids. The lenticular markings in these are generally on the walls 
which lie in planes at right angles to those of the medullary rays and are 
much smaller in diameter. The lines crossing the page represent the 
medullary rays, the upper one showing a resin-duct in longitudinal sec- 
tion, the cells of which are very delicate. The marginal cells of the 
medullary rays are decidedly irregular, and are more or less serrated ; 
the center rays have two to four thin places opposite each cavity of the 
tracheids; but in the transverse section, where the latter are in contact 
with the medullary rays, it can be seen that the inner and next lamella 
are not continuous ; the same feature occurs in the White Pine. 
In the tangential section are seen the openings of the medullary rays, 
which, except those inclosing the resin canals, are of single rows of 
cells, one to eight being superimposed oue above the other in the bun- 
dles ; the marginal cells are the darker spots above and below the cen- 
tral portion of each bundle. In these sections the lenticular markings 
are seen to be very abundant on the cell- walls. The interlacing of the 
tracheids is also well shown. On the right is seen an opening of a resin- 
canal in the medullary system. In the duramen the medullary cells 
are more or less filled with resinous products, which makes it difficult 
to force fluids through these rays into the central portion of the stick ; 
and in the ground, too, the moisture penetrates longitudinally much 
* See Transverse section Larix Americana, p. 51. 
