INTERNAL STRUCTURE OF PLANTS. 
25 
connected in its first formation, and did the separation into 
fibres only take place subsequently ? I shall demand proofs 
if this question is ansAvered in the affirmative ; and if in the 
negative — if the fibre is assumed to be separated from the 
membrane immediately at its first formation — I shall then ask 
further, What difference is there in saying, the fibre is a 
peculiar independent tissue ; or, a membrane is peculiar, 
and primitively separated into fibres ? The word “ deposit- 
ing” does not explain any thing; on the contrary, it has the 
improbable unproved meaning, that the formation of the 
fibre and of the membrane was a mere act of precipitation. 
Even when the fibre is pressed rather flat, it has no simi- 
larity with the parts of a membrane ; for, on magnifying 1500 
times tissue from very young roots, the tender fibres of the 
spiral vessels may distinctly be seen rounded on the edges. 
The enclosing external membrane at that period is so tender, 
that it cannot be perceived. I should like to reverse the 
matter and to say. Whoever investigates the development of 
spiral vessels and of spiral cells, must acknoAvledge the fibre 
to be a peculiar independent formation. With regard to the 
pores, I am of Mold’s opinion, that the opening is covered 
with a tender membrane, and as I could not comprehend how 
it was, that a secondary deposit could be absent from certain 
localities, I thought these places were little bubbles, such as 
are seen in a glass. This, hoAvever, was a mere conjecture. 
My delineator always denied the existence of this membrane. 
At last I was in hopes of convincing him : we saAV it coloured, 
as it is represented in Icon. Select, part i. tab. v. fig. 6, 7. But, 
afterwards, I never saAV any thing of the kind, and the micro- 
scope which I made use of had the quality of colouring objects 
under certain circumstances. Herr Schmidt still maintains, 
that the pores penetrate the walls ; and if we are of a different 
opinion, my opinion, as a preconceived one, must be doubted. 
I likewise not unfrequently observed, especially at the edge 
of the pores, that several membranes of the same kind were 
situated one above another. This may often be seen very 
distinctly in the tubes of the liber. See Icon. an. Bot. F. 1, 
table 6, fig, 15. Payen’s experiments prove, that the deposits 
417 2 D 
