THE 
NEW PHYTOLOGIST 
Vol. XXI, No. 2 25 April, 1922 
PERMEABILITY 
By WALTER STILES 
CHAPTER VII 
THE CELL WALL 
I T is characteristic of the plant cell as contrasted with the animal 
cell that the living protoplasts are surrounded by what is generally 
regarded as a non-living envelope, the cell wall. Certain plant cells, 
such as some unicellular algae, spermatozoids and egg-cells are with¬ 
out this envelope, while some animal cells possess a very definite 
membrane surrounding them, such as the unicellular Vorticella and 
the eggs of some marine organisms. 
But quite apart from the cell wall which forms an undoubted 
membrane surrounding the protoplast, it is the general opinion of 
botanists and physiologists that a membrane surrounds the proto¬ 
plast, separating the general body of it from the cell wall. To this 
supposed membrane a variety of names have been given, of which 
external plasmatic membrane, plasma-membrane and ectoplast are 
those most usually employed. A similar membrane, the internal 
plasmatic membrane, tonoplast or vacuole wall is also recognised 
(de Vries, 1885) and there are even supposed to be similar membranes 
around the nucleus and all cell inclusions (see e.g. Vonwiller, 1918). 
On the other hand, some workers, principally those interested in 
animal cells, deny the presence of such membranes altogether. As 
the nature of the cell membranes is obviously a very fundamental 
matter in regard to cell permeability, some little space will here be 
devoted to a consideration of the cell wall, while in the next chapter 
consideration will be given to the evidence for the existence of 
plasmatic membranes. 
Phyt. XXI. II. 
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