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 Mammillarice, &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 w ithout 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 europcea, Prunus Padus, &c. An allied 

 phaenomenon is also found in the epidermis of the pericarp of 

 Helleborus foztidus. 



The most important of these views I had already expressed 

 in my memoir, " Contributions to our Knowledge of Phyto- 

 genesis," in ( Midler's Archiv. fiir Physiologie/ 1838*. 



But recently have I been able to take in hand MohPs 

 " 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. 



f 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. — Edit. 



