THE STEM OF PLANTS. 45 
4 
t, EM. Then follow three groups of Ligneous fibres, FB; the wood 
vessels, vp, are placed alternately with three groups of woody 
fibres. The bark, enclosed by the line marked 3, succeeds these 
substances, the fibres of the /iser being represented by the letters 
Fc (cortical fibres), and the elements of the suber by the letters Es, 
the laticiferous vessels by the letters vx, and the herbaceous layer 
by the letters nc, the epidermis, EP, bristling with hairs, forming 
the external surface of the trunk. The medullary rays are plainly 
enough observable on the horizontal edge; they commence with 
the pith, and stop with that part of the wood which belongs to the 
EP &S “Ee” EC 
vp RE VP RN VP PB | ae 4 
. Fig. 51.—Transverse sectiou of the trunk of the Maple, fax 
second year’s growth, as indicated in the vertical section by the 
letteks RM. 
Having reviewed all the constituting elements belonging to the 
trunks of forest trees with membranous leaves, we have now to speak 
of the structure of the stems of evergreen trees. Evergreen trees 
(Pines, Firs) are at once easily distinguished from the trees we have 
been considering by the structure of their wood, which is exclusively 
formed of large fibres, without any appearance of thick vessels. 
These woody fibres (Fig. 52) present besides the singular peculiarity 
of exhibiting on each of their lateral faces—namely, those which | 
look towards the medullary rays—a row of dots or punctations, each — 
