20 REPORT ON BOTANY, MDCCCXLI : 
is the period of their production and isolated independent 
development, the membrane forming them, grows in its whole 
substance through intussusception. As soon, however, as the 
cells have joined the cellular tissue as the constituent matter 
of a certain plant or its parts, that kind of growth ceases, 
or, at all events, retrocedes very much. But a new and im- 
portant circumstance is now added to the other phenomena, 
namely, that a new layer is deposited upon the whole internal 
surface of the wall of the cell, in the form of one or more 
bands, closely twisted together, so that the spires exhibit the 
most exact contiguity without any continuity among them- 
selves. Originally, such is the opinion of the author, two 
bands existed together, arising from an ascending and de- 
scending current of the formative matter. The author first 
of all contemplates the case, when the cell has not attained its 
perfect development, at the period when the thickening of its 
walls commences through means of spiral deposits. We find 
here the following cases : — a. Simple fibre (double in the 
sense stated above). The cell extends itself considerably from 
the moment of its production, individual spires grow together 
early, and others become disunited and form annular ducts. 
The author subsequently expresses himself more distinctly, by 
stating, that this laceration or separation takes place by means 
of resorption, b. Simple or manifold fibre, with an extension 
of the cell, and slight or no connection with the wall of the 
cell. Spiral vessels, capable of being unrolled, with wide 
spires, c. Simple or manifold fibre, with a more considerable 
extension of the wall of the cell ; which are generally closely 
grown together. Narrow spired (not X) spiral vessels, that are 
capable of being twisted, false trachese, and partially banded 
and scalariform vessels of the older writers, d. Manifold 
fibre, with moderate extension of the cell ; particular portions 
of the spire grown together ; generally, also, they adhere to 
the wall of the cell. The entire series of forms, from the so 
termed branched spiral, to the reticulated vessels. A portion 
of the banded and scalariform vessels of the older writers 
also belong to this division. The author then proceeds to 
the second case, stating : — If the cell, however, has already 
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