INTERNAL STRUCTURE OF PLANTS. 
21 
attained its perfect development at tlie period when the spiral 
deposits commence, a new and most wonderful circumstance 
takes place, namely, the formation of air vesicles on the out- 
side of the cell, between two adjacent ones, which precedes 
the production of the deposits, and the spires in the inside 
at the locality, which corresponds to the place of those air 
vesicles, separate themselves from each other in the shape of 
fissures. All porous cells and vessels belong to this division ; 
likewise, however, a portion of the former banded and scalari- 
form vessels, which are only distinguished by the length of the 
slit of the pore, from the so termed porous vessels. The author 
further alludes to the difierences of the cells as to form, which 
pass from the small globular to the very lengthy form. The 
vessels, according to his opinion, are produced by the inter- 
vening walls of the cells being absorbed; he also says, that 
the perforation of the primary membrane, in the leaf cells of 
sphagnum, is produced by resorption. The author likewise 
adds, that it is not always only a single deposit that remains, 
but several repeated, and in such a manner, that they either 
lie one upon another, by which the broad plates in the sphag- 
num cells are produced, or when this does not take place, as 
in the pores of Taccus haccata. Previous to this, appeared a 
treatise by H. MoTil, in the same Journal, vol. xxii. p. 81, re- 
specting the structure of the vegetable cell membrane, which 
is particularly directed against Meyen’s opinions ; and, among 
others, against the opinion, that the membrane of cells is 
formed of spiral fibres. In this treatise, he also maintains the 
opinion, that the fibres and punctations of the cells originate 
from a deposit of a secondary, upon the external membrane, 
in many cases even from a tertiary membrane. He believes, 
the process of formation of the simple, particularly of the 
secondary cell membrane, is governed by the rule, that the 
organic substance is not deposited perfectly uniform, but is 
deposited in some places in larger, in others in smaller quan- 
tities ; and it is when this unequal deposit occurs at some 
places in larger quantities, and is entirely wanting between 
the deposits, that these large deposits either (particularly in 
lengthened cells) take place in the direction of a spiral, or 
413 
