174 BOTANICAL GAZETTE | [SEPTEMBER 
attraction of colloids, cause the water to enter with almost as great 
initial rapidity as when pure water is used, until the osmotic pressure 
of the salt on the outside balances the internal forces mentioned; 
then the entrance of water quickly ceases. After equilibrium is 
established in any given salt solution, increasing or decreasing the 
density of the solution extracts water from the seed or permits 
water to enter it in accordance with the direction of the disturb- 
ance. The adjustment continues rapidly after the disturbance until 
the equilibrium is reestablished, when the — again remains 
constant. 


Fic. 2.—Curves showing entrance ‘and withdrawal of water in Xanthium ‘ed on 
shifting pa water to salt solutions, or vice versa, at three-day intervals; the semi- 
permeability of the membrane is well illustrated by the behavior recorded in these 
curves; curves 2, 3, and 4 are displaced to the right to avoid confusion. 
The speed with which this adjustment of internal and external 
forces takes place in Xanthium is again in contrast with the rate of 
adjustment in grasses, such as wheat and barley, in which the rate 
of adjustment is slow, requiring days rather than hours to establish 
equilibrium. It appears that the coat in Xanthium offers very slight 
resistance to the passage of water, while in the Gramineae a com- 3 
paratively much greater resistance is offered by the coat structures. 
This relation of osmotic pressure to capillary and imbibition 
forces, chemical and physical, through the semipermeable coat of 
the Xanthium seed, is splendidly illustrated by figs. 1 and 2, which 

