2 Winter Wheat Varieties and Winfr r-Killing 



place on thawing, and might be prevented by warming very slowly, 

 allowing time for rcabsorpHon of the water by the cell. 



Later Miiller-Thiirgau(:«) proved that this ice formation in the 

 tissues was necessary for freezing to death, and concluded that death 

 was due to the consequent desiccation of the protoplasm. This 1i ypothesis 

 received support from Matruchot and .Molliard (2fi), who demonstrated 

 the identity of the modifications in cell structure produced by frost, 

 plasmolysis and desiccation. The work of (ireeley(iT) supplied similar 

 evidence. MezOi) opposed the theory of death by desiccation, since his 

 investigations indicated that all solutes crystallise out at a temperature 

 not lower than — G C. He concluded that cold desiccation must there- 

 fore be complete at this temperature, and cannot explain injury to plants 

 which resist much lower temperatures. He advanced instead the theory 

 of a fatal minimum temperature for each plant. 



Gorke (14) showed another important effect of the withdrawal of water, 

 namely, the precipitation of certain proteins by the increasing con- 

 centration of the cell sap, aided by its increasing acidity on cooling. He 

 also showed that the precipitation occurred at varying temperatures for 

 plants of varying degrees of hardiness. This was ascribed by Scliaffnit(i(i) 

 to the splitting in varying degrees during the hardening process of 

 com])le.\ proteins into simjiler. less readily precipitated forms. 



Lidforss (2(!) found most hardy plants to have their starch reserves 

 converted to sugar during the winter, and beheved this an adaptation 

 for cold resistance, the sugar having a protective action in preventing 

 the precipitation of the proteins. Schaffnit ( lo) tested the effect of adding 

 sugars and various other substances to plant saps and to egg albumen 

 solution, and was able to modify very greatly the precipitation by 

 freezing. Equally striking results were secured by Ma.\imov(:<0) in 

 increasing the hardiness of sections of red cabbage and Tradescantia by 

 freezing them in solutions of either organic or inorganic substances, 

 provided these were non-to.\ic and had a low eutectic point. 



Recent Progress. 



Recent inve.stigations have dealt nuiinly with the hypotheses noted 

 above, extending them in several important respects. Attempts have 

 also been made to determine the correlation of various physical, chemical, 

 physiological and morphological characters with apparent frost hardiness. 



Several workers have drawn attention to the possible importance of 

 the fact that plant sap is contained in cells of capillary dimensions. 

 D' Arsonval (3) estimated the osmotic pressure in very small cells at 



