Spiral Formations in the Cells of Plants. 43 



sion of the three layers in the formations we meet with in the 

 ligneous cells of Taxus, in the so-called vessels of the Lime, 

 &c. Undoubtedly the primary simple cellular membrane 

 here also constantly forms the outer layer, as to which I agree 

 with Mohl, and no doubt can remain in the mind of the careful 

 observer, that with regard to time the spiral fibres are earlier 

 formed than the porous layer. But I am rather inclined to 

 doubt MohPs statement that this latter is developed between 

 the primary cellular membrane and the spiral fibre layer. 

 Mohl brings forward no reasons in support of it ; and this 

 whole hypothesis seems to me entirely unnecessary, and if only 

 on that account to be rejected. There is no fact which re- 

 quires such an admission for its explanation ; but many, on 

 the contrary, speak against it. Since the cellular membrane 

 itself passes in forming, like all secondary depositions, in the 

 same manner from a fluid through a semi-fluid state to a 

 slighter or greater firmness, a period must necessarily occur in 

 the process adopted by Mohl, during the origin of the porous 

 layer, in which the spiral fibrous layer must be as good as 

 entirely separated from the original cellular membrane, by 

 the newly-formed still semi-fluid layer ; or at least could be 

 separated from it by the gentlest manipulation. But I have 

 never been able to notice a trace of this in Taxus ; and in 

 Tilia exactly the contrary occurs, in so far as here in the cam- 

 bial cells the spiral coils which then still lie densely together, 

 are, it is true, to be unwound with difficulty ; but as soon as 

 the development of the cell begins, and long before the occur- 

 rence of pores, they are already firmly united with the mem- 

 brane. The contrary likewise appears to me to result from 

 an accurate investigation of the above-mentioned cells on the 

 germen of Helleborus fcetidus. 



Also with regard to the porous cells of the Conifer a, I 

 differ in some minor points from M. Mohl. It is true I 

 concur in the main point with MohPs exposition in refutation 

 of Meyen's theory ; but I must nevertheless confess that I 

 think I have seen how in Pinus sylvestris the cells of the 

 cambium, even in the latest annual rings, are constantly di- 

 vided by delicate black lines into narrow spiral bands pre- 

 vious to the formation of pores, (as matter of course with 

 perfect homogeneity of the primary cellular membrane,) and 

 how these, which I regard as the boundaries of the adjacent 

 convolutions, first disappear on the formation of pores ; proba- 

 bly glued to one another in a similar manner as the cells them- 

 selves, whose boundary lines likewise frequently become in- 

 visible in more advanced age ; for when I isolated the cells 

 by boiling in caustic potash, even those from the outermost 



