Permeability 145 
green, appeared to be the same in the surface layer as in the general 
body of the cytoplasm. In adult somatic cells, where the general 
mass of the cytoplasm is in the gel state, it is not possible to dis¬ 
tinguish a differentiated outer layer. 
The peripheral layer of gel observed by Chambers in young germ 
cells, egg cells and Protozoa, appears to be the hyaloplasmic border, 
and in the case of the Protozoa it is definitely spoken of as the 
ectoplast. Seifriz (1921) has, however, recently made a special study 
of protoplasmic membranes by the microdissection method, and con¬ 
cludes that in A mceba and the plasmodium of Myxomycetes the hyalo¬ 
plasmic border is not to be regarded as the plasma-membrane, for 
there is evidence of a definite, though exceedingly delicate membrane 
limiting the hyaloplasm on its outer side. It is shown that the surface 
of a young and active pseudopodium is liquid, for if the hyaloplasm 
is pierced by a microdissection needle and this moved towards the 
edge of the protoplasm, the hyaloplasm will follow the needle so as 
to form an artificial pseudopodium, while on releasing the needle 
there is no appreciable contraction. This behaviour is only explicable 
on the view that the surface layer is liquid. But after the pseudo¬ 
podium has advanced to a certain point, there is no further advance, 
to explain which it is supposed that a sudden change in consistency 
of the protoplasm from sol to gel takes place. This change must be 
at the surface, for the hyaloplasm changes little in viscosity. The 
surface layer of gel is now capable of a little stretching. This is the 
condition of a quiescent plasmodium. Seifriz thus concludes that 
“the inactive surface layer is a highly viscous emulsion colloid, un¬ 
doubtedly in the gel state, which solates (i.e. becomes a sol) when 
streaming takes place, and reverts to the gel state when the plasmodium 
again becomes inactive. This surface layer is exceedingly delicate, of 
immensurable thickness, and is not identical with the hyaloplasmic 
border (or ectoplasm), which, to be sure, it resembles in constitution, 
but from which it is more or less sharply delimited.” The state of 
affairs in A mceba is similar except that the hyaloplasm (ectoplasm) 
behaves in the same way as the membrane, though in the passive 
condition it is less rigid than the membrane and so can be distinguished 
from it. 
From the fact of the regeneration of the plasma-membrane from 
cytoplasm containing hyaloplasm, it is concluded that the membrane 
is formed from the latter and is certainly not to be regarded as an 
autonomous organ as de Vries (1885) supposed. 
In dead material a delicate membrane can sometimes be observed 
Phyt. XXI. Ill 
10 
