238 BOTANICAL GAZETTE [SEPTEMBER 
This alteration he supposes to be the production of complete 
permeability. Sztics (61) has since stated that the alteration 
consists of a hardening of the protoplasm, since centrifuging no 
longer displaces the cell contents. He also found the “hardening” 
to be temporary, and to be followed by “‘reliquefaction.” 
LEPESCHKIN (27) claims to determine with great accuracy, by a 
method based upon the difference in the osmotic pressures of 
isotonic plasmolyzing substances, the absolute rate of penetration 
of these substances. It is impossible to explain the method clearly 
and at the same time briefly, but its essential features are as 
follows: a comparison of the osmotic pressure of a saccharose 
solution which will just cause visible plasmolysis, with that of a 
glycerine solution which, following the saccharose, will cause no 
change in volume (as determined by LEPESCHKIN’s criterion) shows — 
_ the latter to be the higher. If we let u represent a factor propor- 
tional to the permeability of the protoplasm to the glycerine, and 
assume that the protoplasm is impermeable to saccharose, then 
| =e, » where C” is the concentration of glycerine found to be 
isotonic with the saccharose solution, and C the concentration 
calculated to be isosmotic with the saccharose solution. For 
saccharose we may substitute any substance to which the proto- 
plasm is supposed to be impermeable, and for glycerine any inkl 2 
stance whose rate of penetration it is desired to measure. 
This method would be exact provided the following assumptions — 
were in accord with the facts: oe the prtogsm 5 is impermeable 
to the control substance (in this case ; (2) neither of the 
substances used causes any alteration i in the permeability of the 
protoplasm; (3) no exosmosis occurs. All these assumptions are 
_ rendered highly improbable by the evidence already secured by 
_ other methods, and additional evidence against their validity will . - 
. be submitted by the writer in a subsequent paper. 
LEPESCHKIN also appears to assume that there is an effect on ss 
me ie water equilibrium caused by the simultaneous age ee - 
eee et he aed dependent 
