1913] SHULL—SEMIPERM EABILITY OF SEED COATS 195 
theory of. the structure of water has not been well received by 
American chemists; perhaps it has not been given the attention it 
deserves. As regards its application to the problems of semi- 
permeability there seems to be some difficulty. The data obtained 
at one point with Xanthium seeds argue against the hydrone theory 
as a universal explanation. 
For instance, Brown found that both NaCl and AgNO, failed to 
penetrate the coat of Hordeum. ARMSTRONG says in effect that the 
membrane is hydronated, both salts are hydronated, therefore they 
do not enter, although the water in which they are dissolved may 
enter freely. In my experiments NaCl does not pass through the 
Xanthium coats, therefore both salt and membrane must be hydro- 
nated. Now if ARMsTRONG’s theory is correct, a solution of AgNO, 
should also be excluded, for BRown’s experiments have shown that 
AgNO, is a hydronated salt when in solution. But this does not 
happen, for silver nitrate is retarded but slightly, whereas according 
to ARMSTRONG’s hypothesis the mutually hydronated surfaces 
should attract each other so strongly as to prevent the passage of 
the salt. Trichloracetic acid was exceptional in its behavior in 
BRown’s experiments, so that the hydrone theory cannot as yet 
be accepted as a general explanation of selective semipermeability. 
More facts are needed before the physiological semipermeability 
of living or the physical semipermeability of non-living membranes 
can be adequately explained. 
Further studies on the seed coats of Xanthium and other seeds 
are being continued. The microchemistry of the coat, its relation 
to oxygen diffusion in respiration, its relation to the impermeability 
of “dry” solvents, and its use as a measure of surface tension forces 
in soils are now under investigation. The earlier results of these 
Studies cannot of course be presented at this time. 
IV. Summary 
1. The dry seed coats of Xanthium are impermeable to dry 
alcohol, ether, chloroform, and acetone. BECQUEREL’s results with 
the coats of other seeds are confirmed. 
2. Evidence of the diffusion of oxygen through absolutely dry 
seed coats was not obtained. 
