38 



Dr. M. J. Schleiderr'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- 

 scribed 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 an end 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 Tiijfel for Pore. — Edit. 



