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tical ray. It is difficult without the aid of a diagram to 
convey a clear idea of the sequence in which the various 
portions of bark and wood are formed; suffice it to say 
that each successive addition of bark is projected into the 
wood a shorter distance than its predecessor, and as the 
innermost extremity of every plate is truncate or rectan- 
gular, it follows that the outline presented by each cortical 
mass is that of a pyramid, whose sides are formed of a 
series of rectangular steps like an ordinary stone staircase. 
It is difficult to account for this singular appearance, but the 
more probable explanation seems to be that a layer of wood 
is deposited for every layer of bark, so that by the time a 
new deposition of the bark is about to take place the wood 
has already surrounded the extremity of the previous plate, 
in consequence of which the progress . of the new plate 
inward is barred by the previous season’s layer of wood. 
If this explanation be sound the number of cortical plates 
on one side of, and including the primitive cortical ray, in- 
dicates the age of the stem under examination. Each 
annular layer of wood is thus broken up into four distinct 
portions by the projecting bark, each portion filling up one 
of the spaces enclosed by two of the arms of the cross. The 
number of plates formed on each side of the four primitive 
cortical rays rarely exceeds six. The peculiarity of ar- 
rangement, to which I here draw attention, is so striking, 
that it is a matter of surprise to see this feature so badly 
represented in Gaudichaud’s plates; it is fairly drawn by 
Schleiden, in his Principles of Botany (pp. 251-252 of the 
English translation,) but a better figure is given by Du- 
chartre, in his Elements de Botanique, p. 167. 
Another arrangement of the cortical portion is also 
common. It commences, as in the last method, with the 
projection of four slender rays into the midst of the woody 
fibres, reaching about half way to the pith ; but the 
next additions which take place are not found by the side 
