14 



scribed by Muller-Thurgau with reference to the freezing of the cell 

 water in the intercellular spaces, rather than within the cells. Both 

 Muller-Thurgau and Molisch hold the view that freezing to death 

 results from the rapid withdrawal of water from the cells to form 

 these ice crystals in the intercellular spaces. 



Matruchot and Molliard 1 observed that water is extruded from 

 the nuclei of plants that have been frozen, dried or subjected to the 

 action of solutions of high osmotic concentration. 



Gorke has recently offered an interesting theory as to the cause 

 of death by freezing. He found that when the plant sap is frozen, 

 certain proteids may be precipitated out and apparently those plants 

 that are most easily killed by freezing have their proteids precipitated 

 out at the highest temperature. Thus begonia, which is very easily 

 killed, had its proteids precipitated at -3° while sap from pine needles 

 required a temperature of -40° to precipitate any proteids. Gorke 2 

 assumes then that killing from cold may be due to the precipitation 

 of the proteids, and accounts for this precipitation by the greater 

 concentration of the salts in the sap as water is removed to form ice 

 crystals. It is well known that certain proteids can be precipitated 

 out by increasing the concentration of salts, especially zinc sulphate 

 and ammonium sulphate. Gorke made up solutions of albumen 

 with zinc sulphate and found that after freezing to -20° there was a 

 large precipitation of proteids. 



Lidforss 3 working with the wintergreen plants of South Swed- 

 en, has found that with most of them at least during cold weather, 

 the starch is almost entirely changed to sugar, though on the return 

 of warm weather starch may be again deposited in the cell. He 

 assumes that this sugar is formed during cold weather as a means 

 of protecting the plant against freezing by lowering the freezing 

 point of its sap. He was able also to increase the resistance to low 

 temperature of the leaves of wintergreen plants and the roots of 

 Zea Mays by keeping thegj-for a time immersed in S to 10 per cent 

 sugar solutions. 



Schaffnit 4 , following the work of Gorke, found that the pro- 

 teids of rye grown in the open at low temperatures are not readily 

 precipitated by freezing, while the same temperature will readily 

 precipitate proteids from sap of rye grown in the greenhouse at muclr 



'Compt. Bend. Acad. 8d. Paris, Vol. 132 (1901) pp. 495-8. (Bibl. No. 71a> 



'Land. Versuchs. Vol. 65, p. 149, 19.06. (Bibl. No. 47). 



8 Lunds TJnlversitets Arssk., Vol. 2, No. 13, 1907 (Bibl. No. 62); Bot. Centlb., Vol. 68 

 No. 2, p. 33. (Bibl. No. 63). 



4 Mitt. Kaiser Wilhelm Inst. Landw. Bromberg, Vol. 3, No. 2, pp. 93-115, (Bibi. No. 

 98); Zeits. f. AUg. Phys., Vol. 12, pp. 323-36. (Bibl. No. 99) 



