Spiral Formations in the Cells of Plants. 37 
least two such bands present*, whose extremities at the end 
of the cells pass into one another, and in most cases, even 
very early, cohere inéer se to a single one. 
Hence, then, proceed all the varied formations of the cells 
and vascular walls, according to the different influence of the 
following momenta. 
_ A. The most essential circumstance, in my opinion, upon 
which is also founded the division of all these textures into 
two large principal groups, that of the Spiroidea (I borrow 
this expression, which is very useful, from Link), and that of 
the porous formations, is the following : 
Either the cell has, at the time when the thickening of its 
wall by spiral deposition commences, already attained its 
complete expansion, or not. 
I. Let us, in the first place, consider the latter case. Here, 
then, a second momentum becomes of importance; it is the 
cohesion both of the fibre and the cellular wall, and of the coils 
of the fibre infer se; at the same time, therefore, the number 
of fibres is likewise of value. 
a. Simple fibre (double in the sense above stated). The 
cell still expands considerably from the instant of its origin ; 
some conyolutions cohere early, others tear asunder: annular 
vessels (of which a more detailed description below). In this 
case the fibre is generally not at all, or but loosely united with 
the cellular membrane. 
6. Simple or compound fibre, a still rather considerable 
expansion of the cell, slight, or no cohesion with the cellular 
membrane: spiral vessels with broad convolutions, capable of 
unrolling. 
e. Simple or compound fibre, extremely slight expansion 
of the cellular membrane, generally intimate cchesion with it : 
narrowly wound spiral vessels capable of unrolling, false tra- 
chee, and in part the striped and scalariform vessels of older 
writers. : 
_ d. Compound fibre, moderate expansion of the cell, cohe- 
sion in some places of the convolutions inter se, generally 
also with the cellular membrane: the whole series of the 
forms of the so-called ramified spiral vessels to the reticulate. 
Hereto likewise belong a portion of the striped and scalari- 
form vessels of the older writers. 
In these last, as well as in all the preceding, the law, that 
the more intimately the fibre coheres with the cellular mem- 
brane, the less this can expand, appears to obtain. 
* Corresponding to an ascending and descending current of the mucous 
formative substance. 
