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, 
&e. 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 Mohl’s 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 séparated 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 Jarvus; and in 
Tila 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 fetidus. 
Also with regard to the porous cells of the Conifere, I 
differ in some minor points from M. Mohl. It is true I 
concur in the main point with Mohl’s 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 
pect homogeneity of the primary cellular membrane,) and 
ow 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 
