532 BOTANICAL GAZETTE [JUNE 
tissue (5 cm. long) is only 392? No doubt an explanation of this 
is forthcoming, but it has not been given so far, and it will serve 
to indicate the necessity for a full description of OsTERHOUT’S 
apparatus and method before his conductivity measurements of 
tissues can be accepted by other workers. 
Finally, there is the question as to whether the electrical 
conductivity of tissue can be used as a measure of permeability. 
Can it be assumed that the electrical conductivity as measured by 
KouLRAuscH’s method is really a measure of the permeability of 
the protoplasm to ions? We have already called attention (12, 13) 
to the fact that the conductivity of tissue is the resultant of the 
conductivity of a variety of different phases, and owing to the 
complex arrangement of these phases it cannot be assumed that 
the conductivity of the whole is the sum of the conductivity of 
each phase. H6BER (2, 3), using a method which it is true is 
perhaps not above criticism, comes to the conclusion that the 
interior of the cell only contributes relatively slightly to the total 
conductivity. Moreover, OsTERHOUT neglects the fact that if the 
penetrability for ions increases, a necessary consequence of this 
may be increased diffusion between the external medium and the 
interior of the tissue, resulting in changes of concentration in the 
interior of the cell. Similarly, any change which altered the con- 
centration or the distribution of free electrolytes in the interior of 
the cell would alter the conductivity. It may be, although we do 
not certainly know, that electrical conductivity gives a rough idea 
of the permeability of the cell; it is extremely unlikely that it gives 
numbers so exactly proportional to any kind of permeability that 
“temperature coefficients of permeability” can be calculated from 
them. Hence we consider it impossible to accept any of OSTER- 
HOUT’S results obtained by his electrical conductivity method with 
Laminaria disks until (1) he makes clear what he means by per- 
meability when this word is used in a quantitative sense; (2) he has 
given proof that his method does give values for the electrical 
conductivity of the tissue employed; and (3) he has produced 
evidence that the electrical conductivity of tissue can be taken as 
a measure of permeability in the sense in which he uses that word. 
We should also like to raise two further points arising out of 
OsTERHOUT’s work. In the first place, we would point out that in 
