I l6 THE PLANT WORLD. 



the water will move through the cell wall until this increase in 

 imbibition force is equalized. For this purpose water will be 

 taken from the inner wall layers, thus increasing their power of 

 imbibition. They in turn will be supplied by water from the pro- 

 toplasm, and this in turn by the cell sap. In other words, a read- 

 justment of equilibrium will occur throughout the whole svstem. 

 As crystallization progresses, more and more water will be ab- 

 stracted from this system until finally the force of imbibition 

 becomes sufiiciently strong to equilibrate the molecular force of 

 crystallization, at which time the growth of the crystal necessarily 

 ceases. Not all the water passes from the cell on freezing, but 

 only a part of it. depending upon this equilibration of forces. No 

 further freezing will now occur unless the temperature again falls, 

 thus causing an increase in strength of the force of crystallization. 

 More water will then pass to the crystal until equilibrium is again 

 established. 



Naturally the greatest quantity of water which will move 

 through the wall to equalize the disturbance in the system will 

 come from the regions where the force of imbibition is least, 

 namely, from the cell sap. Consequently, in freezing, the sap is 

 the first to lose water, then the protoplasm, and finally the cell 

 wall. The quantity of water lost is greatest from the cell sap and 

 least from the cell wall. The quantity of water in the protoplasm 

 will not decrease until the force of imbibition in the cell sap 

 reaches in intensity that acting upon the molecules of water held 

 weakest in the protoplasm. ^A. like relation will exist between the 

 protoplasm and the cell wall. Even after water has begun to be 

 extracted from all these layers the larger quantity will for some 

 time continue to be extracted from the sap and protoplasm. The 

 greater quantity of the water to form the ice crystals in plants 

 therefore comes from the cell sap and the next largest quantity 

 from the protoplasm. 



(b) It may be assumed that the crystal actually draws water 

 toward itself. This it might do in this way. The water through- 

 out, not only the cell, but the whole adjacent tissue may be con- 

 ceived to be a connected whole possessing an adhesion and rigidity 



