144 
Sydney H. Vinks. 
of the beet-root. He found that, after remaining for fourleen days in wa¬ 
ter, they allowed neither their colouring matter nor tbeir sugar to escape. 
llis further experimenls') demonstrate still more clearly the importance 
of this protoplasmic layer in producing a turgid condition of the cell. 
Bj placing growing cells in Solutions of different salts, especially in So¬ 
lutions of saltpetre, which were more coneentrated than the cell-sap, 
he was able lo diminish the turgidity of the cells, and when the solu- 
tion contained as rnuch as ten per cenl of the salt, the protoplasm con- 
tracted away from the cell-wall and the turgidity of the cells was en- 
tirely removed. To Ibis condition he gives the naine of »Plasmolysis«. 
llis experiments do not, however, merely demonstrate Ibis important 
function of the protoplasm, but they also prove the absolute necessity of 
a turgid condition to the growth of a cell. He found, that immersion of 
the cells in strong Solutions of salts for a sufficient time to produce com- 
plete plasmolysis, did not kill the cells, and that, if they wcrc placed in 
water, the salt was gradually removed, the protoplasm slowly resumed 
its formet' position. The growth of branches, peduucles etc., was more 
or less diminished when they were placed in the more dilute Solutions, 
and was entirely arrested when the Solutions were sufficienlly concentra- 
ted to cause complete plasmolysis of the cells. After thorough washing 
in water they resumed their growth. 
Frotn diese observations it is evident that this protoplasmic layer is 
very extensible. The fact, that it is impermeable to the cell-sap contai¬ 
ned in the vacuole, which it surrounds, and that the cell-sap, by virlue 
of its endosmolic properties, ever tends lo increase in quanlity, justities 
the conclusion that, under normal conditions, the protoplasm of a gro¬ 
wing cell is in a state of tension. So long as it yields to the pressure 
from within, growth is possible, but shouid its extensibility be so dimi¬ 
nished that it completelj neutralises this pressure, growth must ccase. 
The cell-wnll may be regarded as being completely passive in this pro- 
cess. It is stretched by the lense protoplasmic layer by which it is lined, 
but is, of itself, incapable of so resisting the escape of the cell-sap as 
lo cause any turgidity of the cell. 
It may be concluded, therefore, that the retardation of the growth 
of the hypha of Phycomyces, produced by the aclion of light, is to be 
attribuled to a diminished mobiiity of the micellaj of the protoplasm ra- 
ther than lo a diminished mobiiity of the micelkc of the cell-wall. It may 
be further inferred, that this holds good also in the case of the growing 
cells of a mullicellular organism. 
This Statement receives considerable support from the facts, which 
are already known as to the action of light upon protoplasm. The so 
t) Unters, über Zellslreckung. 1877. 
