1913] SHULL—SEMIPERMEABILITY OF SEED COATS IgI 
any sound conclusions can be drawn. Semipermeability is now 
shown to be common enough that its existence should be proved or 
disproved before proceeding to use stimuli acting through mem- 
branes such as those referred to here. 
With a number of the solutions used in these experiments a very 
high percentage of increase in weight was noticed, running much 
higher than the imbibition in pure water. This was noticed with 
HgCl,, AgNO,, several alcohols, acetic acid, and especially the 
alkalies. The intake in these , 




1,0 
cases cannot be considered as = »f 
due entirely to imbibition and 7 
capillarity. Several things may *E 
be responsible for the large in- 2 
crease in weight. In the case “— 
of the solutions of the heavy 
metals their specific gravity has ve 
something to do with the great ,[ —— 
. . . . Ae Soll ae) Gs Uy Se Re se eS a Ma 
increase; but there is convincing ee i ee sags 
evidence that this is not the only 
Fic. 9.—Curve showing increase of 
cause. 
The seeds become greatly 
swollen, until in many instances 
they are perfectly cylindrical 
and stretched to inordinate size. 
imbibition force in seeds with decrease 
of water content; percentage of H,O is 
based on absolute dry weight; air-dry 
seeds are considered to have 8 per cent of 
oscopic moisture in this diagram; the 
force as here plotted is based on figures 
discussed in the text. 
In these cases a fluid is found 
between the coat and the rest of the seed. Evidently there is a 
dissolution of various constituents of the embryo whose decompo- 
sition products are osmotically active, which exert great pressure 
upon the coat from within, and which thus cause a very large intake 
of water. This is true especially when alkalies are used. Fig. 9 
shows the curve of increase in weight of seeds kept in molecular 
NaOH. The earlier part of the curve, up to 24 hours, resembles 
the imbibition curve for water, only the entrance is_a little more 
rapid. Then suddenly the weight increases under the pressure of 
dissolved organic substances from within, and by the end of three 
days the outer layers of the coat have been bursted, leaving the 
inner layer intact. Through its translucent cells one can see the 
