38 Dr. M. J. Schleiden’s Observations on 
II. But if the cell has, at the time when the spiral deposi- 
tions have begun to form, already attained its complete ex- 
pansion, a new and highly remarkable circumstance comes 
into action,—namely, that the formation of air-vesicles on the 
outer wall of the cell, between it and the adjacent ones, pre- 
cedes the origin of the depositions; and the convolutions 
forming, closely lying one upon another, and in most cases 
rapidly cohering inter se, separate from one another cleft-wise 
at the place which internally corresponds to those air-vesi- 
cles. Since this process can be followed very far, and can- 
not, merely on account of the minuteness of the parts, be 
followed in several otherwise exactly similar formations, sound 
analogy advises us to extend it to all porous textures. This 
in general merely narrow slit, is often rounded by deposited 
formative substance, on which account the pore* appears the 
rounder the more the cell is developed ; the longer, but more 
cleft-wise, the younger it is. Now to this division belong all 
porous cells and vessels, and likewise a portion of the earlier 
striped and scalariform vessels, which then only differ from 
those called porous by the length of the fissure of the pore. 
B. A further momentum, which will here be but briefly 
noticed is, on the one hand, the form of the cell in the vari- 
ous intermediate stages between the two extremes of the 
small globular, and the much extended in length, in combi- 
nation with an actual perforation of the primary membrane 
by absorption. To this head belong several formations, first 
indicated by Moldenhauer, and then correctly and fully de- 
seribed by Mohl, for instance, the leaf-cells of Sphagnum. 
But hereto more especially belong the difference between 
cellular tissue and so-called vessels, the latter being nothing 
more than cylindrical cells, generally situated in the same 
direction, with the terminal surfaces on one another, the 
septa of which are perforated in the most varied manner by 
absorption. 
C. By far more important, however, is the following. 
Namely, in the vital process of the cell, spiral deposits are by 
no means at anend with the first layer; but they are repeated 
in many cases, almost as frequently as the volume of the cell 
permits. The rule then is, that the successive strata arrange 
themselves entirely according to the first, be this modified by 
the above-mentioned influences as it may, so that the places 
of the cellular wall not covered by the first deposit likewise 
remain free from all the succeeding ones. In this class is com- 
* We have here omitted a note, which relates merely to the employment 
of Tvffel for Pore.—Epir. 
