SECTIONS OF WOODS GROWN IN BRITAIN. 4] 
of the resinous canals in their structure. The general differences 
clearly indicate the genera; and while the distinctive features are 
not quite so constant in the species—the structure of which is 
modified by the soil, situation, and exposure, — still they are 
usually so clear and distinct as to demonstrate the species, and 
in many cases the’ variety. 
In the timber of the pine tribe there are no true vasa, but it 
exhibits numerous pores, which botanists call resinous canals, 
irregularly distributed in groups, or otherwise, in the concentric 
layers or zones, and varying in number according to the species. 
The pores in the duramen or heart-wood are usually in a congested 
state with resin, which prevents the free passage of liquids through 
the wood. Those situated in the alburnum or sapwood are generally 
quite clear and open. In the structure of the arborvite, cedar, 
cypress, yew, and silver fir, there are no resinous canals. 
As already stated, the tissues of the various kinds of wood are 
easily distinguished by the number, size, and position of the vasa 
and canals, together with the density of the zones, and the size and 
number of the medullary rays. The medullary rays in the pine 
tribe are extremely numerous, usually placed in groups (as seen 
in a vertical or radial section), cylindrical in shape, and very much 
compressed. With the aid of the process known as “ photo- 
microphy” this is made quite clear, and illustrations are given 
herewith of some of the leading species, which will explain the 
nature and usefulness of the sections. These illustrations are 
produced from photographs which were taken from the woody 
tissue, and are not of a hypothetical character, consequently 
they are the more valuable for reference. 
The tissue of the timber of conifers is among the simplest and 
most interesting. By reference to the illustrations (Figs. 1 to 7), 
it will:be seen that in its construction it resembles a network of 
rather regular meshes. The wood of the Wellingtonia gigantea 
(Fig. 7) is a good example of this, in which the resinous canals 
are situated at the union of the spring and the previous autumn 
growths, and irregularly arranged in more or less continuous circles ; 
yet at the same point in the growth, the canals are sometimes quite 
absent from several consecutive annual rings. The resinous 
canals of Abies Menziesti are somewhat similar to those of the 
Wellingtonia, but much more constant, and are distributed 
irregularly throughout the whole zone. 
Another characteristic of the structure of coniferous timber is 
