R. Newton IH 



complex of the protoplasm and to increase the permeabihty of the cell 

 by freezing. Since the permeability of the tissues had not been affected 

 by freezing, it was decided to attempt to destroy the colloidal complex 

 and increase permeability by ])lacing the material in a closed pressure 

 flask and heating it in a boiling water bath. The juice was then expressed 

 as readily by the hand press as by the hydraulic press, 30 to -10 c.c. 

 (about the usual amount) being collected from each sample. 



These observations give rise to some very important considerations. 

 In the first place, the wheat plants were apparently not killed by ex- 

 posure to temperatures lower than normally obtain in many places 

 where they suffer severe winter-killing. The specific temperature must 

 be only one of a number of factors involved. It is also apparent that the 

 hardening process continued long after the advent of freezing weather, 

 as this difficulty was not met with in the collection of November 12. 

 Further, and contrary to the findings of a number of workers, hardening 

 was not in this case associated with an increase in the dry matter content, 

 since as already noted the water content was greater in the collection 

 of December 9. Nor was it associated with an increase in sugar content; 

 this value had decreased, as will be seen later. 



Most significant is the evident tenacity with which the hardened 

 tissue grips its water content. Wiegand (18) noted that as the temperature 

 falls the quantity of water separating in the form of ice becomes con- 

 stantly less and less. The same author develops the theory that the 

 passage of water from the cell during freezing is due to an equalising of 

 the force of imbibition, acting from the outer cell membrane to the centre 

 of the system ; this follows as a consequence of the disturbance of equi- 

 librium set up by the force with which the formation of ice crystals 

 takes water from the surface of the cell. Wiegand supports the view that 

 death is due to drying of the protoplasm beyond its critical water content. 

 Evidence of other workers as tu the importance of resistance to desicca- 

 tion has been presented in an earlier section of this paper. Whatever may 

 be the precise mechanism by which withdrawal of water brings about 

 disorganisation of the protoplasm, it seems clear at least that hardiness 

 must be intimately connected with forces which oppose this desiccation. 

 In the light of our present knowledge of the properties of colloids, it 

 seems most probable that the principal force is imbibition. 



Spoehr (45) found that in cacti the pentosans increase with decreasing 

 water supply. MacDougal(37) also points out that the conversion of the 

 diffusible sugars to the mucilaginous pentosans is one of the alterations 

 which may result in the cell as a consequence of partial desiccation. The 



