Spiral Formations in the Cells of Plants. 39 
prised the thickening of the annular and spiral fibres to such 
a degree that they appear as plates, which are placed with 
their narrow edge on the cellular wall; for instance, in the | 
Sphagnum-cells, in the ligneous cells of the Mammillarie, &c. 
Hereto also belong all the porous cells, with septa thickened in 
a stratified manner, for the knowledge of which we are chiefly 
- Indebted to Mohl. 
But we are now already acquainted with some interesting 
exceptions to this rule, namely, that after the first spiral 
deposit has been altered by the expansion of the cell, a 
new layer is deposited on the entire inner surface, on fibre 
and on primary cellular membrane without distinction; but 
since this second layer stands in a different relation to the 
primary cellular membrane from the first, it also must, ac- 
cording to what has been above stated, adopt a different 
form, viz. the porous. These formations of distant fibres, 
between whose convolutions pores are found, are exhibited, in 
fact, by a number of dicotyledonous ligneous cells, especially 
of such plants as are subject to the strong antagonism of the 
period of vegetation and of winter sleep. Thus, for instance, 
Taxus baccata, Tilia europea, Prunus Padus, &c. An allied 
phzenomenon is also found in the epidermis of the pericarp of 
Helleborus fetidus. 
The most important of these views I had already expressed 
in my memoir, “ Contributions to our Knowledge of Phyto- 
genesis,” in ‘ Miiller’s Archiv. fiir Physiologie,’ 1838*. 
But recently have I been able to take in hand Mohl’s 
** Memoir on the Structure of the Vegetable Cellular Mem- 
brane”+, (Tubingen, September, 1837) ; and I found, to my 
very great joy, that we entirely agree in two important 
points: first, in maintaining against Meyen, that every indi- 
cation of a spiral, fibrous, or porous structure, is a certain 
proof that we have no longer to do with the original simple 
cellular membrane; and next, in his position: “ Fibre and 
membrane differ merely by their size, and by the form in 
which they occur,” which essentially agrees with my view 
that the spiral is only a secondary difference of form in the 
product of the vital force (in the fibre substance, or more 
correctly, the membrane substance). The slight chemical 
modification which I have demonstrated in it is, at least, far 
more inconsiderable, and consequently less essential, than the 
* Translated in Taylor’s Scientific Memoirs, Part VI. 
+ The paper here alluded to, and Meyen’s opinion on the same subject, 
have been placed before the English reader in Mr. Francis’s translation of 
Meyen’s Report on Vegetable Physiology for 1837.—Enprr. 
