‘ THE STEM OF PLANTS. 39 
stem of one of our forest trees. It is that assemblage of diverging 
lines which bear the name of medullary rays. In a transverse 
section of the stem of a tree, the mass of wood is traversed by a 
great number of radiating lines, all of which start from the back 
and converge towards the pith, or medulla. But they do not all 
reach it; there is a certain number which stop short in some of 
the layers, more or less deep in the trunk, without reaching the 
pith. These radiating lines result from the transverse section of 
the cellular laminee, the edge of which we thus see, and the length 
and thickness of which are variable. 
cia 
oe 
iM 
Pst NS — 
Shacks secs 
ca OH NH OOO y) : 4 
ROS Y Ls 
RM 
Fig. 45.—Medullary rays of the Cork-tree Fig. 47.—Medullary rays of the Maple. 
(horizontal section). 
Fig. 46 represents the medullary rays of a trunk of Cork-tree 
(Quercus suber), in a transverse section. Fig. 47 shows the same 
organs in a similar section of the stem of the Mapie, magnified by 
means of the microscope. In this last, Rm are the medullary rays, 
which go from the centre to the circumference of the stem. The 
trachew, the ligneous fibres, and the vessels, are represented by the 
