NOTES AND MEMORANDA. 181 
the multiplication of cells by the formation of new cells zn 
their interior as a general law in the vegetable kingdom. He 
was supported by Nageli. The views of Von Mohl, deve- 
loped as they were by Meyen and Unger, eventually estab- 
lished themselves. In a paper on the structure of cork and 
bark, Von Mohl described the nature of the tissues which 
enter into their composition, and accounted for the diversity 
of their character in different plants, especially the exfoliation 
of layers of bark in such trees as the Plane. 
In 1844 Von Mohl maintained, against the theory of 
Dupetit-Thouars, the dependence of the growth of Dicoty- 
ledons on the physiological activity of leaves. The same 
year he published his remarks on the structure of the vege- 
table cell, which for a long time immensely influenced the 
course of vegetable histology. He regarded the cell-well as 
generally composed of a primary external imperforate mem- 
brane, and a secondary one usually perforated with apertures. 
This he supposed to be lined by a third membrane, “ Prim- 
ordialschlauch,” the primordial utricle of English writers. 
“This membrane forms a perfectly closed, cell-like, thin- 
walled vasicle, which in the fresh plant is closely applied to 
the inner wall of the cell, and therefore escapes observation ; 
while in specimens which have been preserved in spirit it is 
contracted, and more or less detached from the wall.” 
Von Mohl’s paper, “ Ueber die Saftbewegungen im Inne- 
ren der Zellen,” published in 1846 (‘ Bot. Zeit.,’ p. 73), has 
been the starting-point of all modern views about the vege- 
table cell. He first described accurately the ‘ opaque viscid 
fluid of a white colour, having granules intermingled with it, 
which fluid I call protoplasm.”’ He observed the vacuoliza- 
tion of the protoplasm until it forms a mere network. He 
described the motion which takes place in the filament of the 
network, “or perhaps now first becomes visible,” and he 
measured its rate. Schleiden gave the theory its finishing 
touch in the third edition of his ‘ Principles’ (1849), by 
identifying Mohl’s primordial utricle and circulating fluid. 
In 1850 Von Mohl published a small work with the title 
‘Die Vegetabilische Zelle,’ which weaves the results of a 
great deal of what he had written in scattered memoirs into a 
continuous whole. It was translated into English by Prof. 
Henfrey in 1852. 
Von Mohl felt the greatest interest in improving the means 
of histological and anatomical research, and wrote several 
papers on the construction and use of optical instruments, 
and in 1846 published a book on micrography. 
