22 REPORT ON BOTANY, MDCCCXLI : 
(especially in shorter cells) in the direction of the fibres of a net. 
There is another treatise in the same volume, p. 673, by H. 
Mold, respecting the annular ducts, directed against Schleiden, 
who asserts (as already mentioned), that annular ducts, which 
are capable of being unrolled, were formed from the basis of 
spiral vessels, the fibres of which have grown together from 
two spires which have become closed, and which subsequently 
become isolated by the resorption of the spiral formed portions 
of the fibres that are situated between. H. Mohl observes, — 
“ I have explained the reasons in the treatise respecting the 
vegetable cell membrane, which are in favour of a fibrous 
structure, belonging to those secondary cell membranes, that are 
distinguished by stripes ; and by a greater degree of capabi- 
lity of tearing or separating themselves in a spiral direction ; 
and by depressions and furrows, which extend themselves 
through the entire thickness of the membrane of the cell ; and, 
in a still higher degree, by fissures.” He considers the struc- 
ture of the fibre, which forms the annular ducts, to be quite 
analogous to the structure of the spiral fibre, and shows, that 
(especially where the rings are situated near to each other), 
in the lines of division, shallow or deeper furrows exhibit 
themselves, which are quite parallel to the edges ; and that 
(where they are more removed from each other) a regular 
spiral fibre runs between them in other cases, which either 
connects itself with the rings or not. This representation 
alone must cause a doubt with regard to Schleiden’s theory. 
A principal reason, however, is the examination of Tra- 
descantia tuherosa, to which Schleiden refers, especially of 
the roots, where (in the first states in which the fibres exhibit 
themselves) they have already the same differences of form, 
viz. : — Annular and spiral fibres, as in the subsequent states. 
This is followed by the preliminary answer of Schleiden, to 
which we have alluded in the commencement. He states, that 
he does not believe that he has been mistaken in his obser- 
vations, but that he has seen real stages of transition, as the 
stationary rings are distinguished essentially by sharpness of 
delineation, firmness, and clearness of substance, from the yel- 
lowish jelly-like transitionary matter of the spiral, which is 
414 
