Killing of Plant Tissue by Low Tempeelature 153 



higher temperatures. He also found that he could prevent the pre- 

 cipitation of proteids from this sap of greenhouse rye by adding to it 

 small quantities of sugar. He concludes then that the formation 

 of sugar in wintergreen plants described by Lidforss may be the 

 means of protecting the plants against precipitation of proteids. 

 However, Schaffnit concludes that precipitation of proteids is the 

 only way by which loss of water during freezing kills plant tissue. 



Maximow^ has recently published three very interesting papers 

 covering work in freezing sections of plants, mainly red cabbage and 

 Tradescantia discolor. Thin sections of tissue from the upper side of 

 the leaves were frozen in solutions of various strengths of both organic 

 and inorganic substances after they had stood for varying lengths 

 of time in the solutions. He found remarkable protection to be ex- 

 erted by both organic and inorganic substances whenever their 

 eutectic point (the temperature at which they crystallize out, giving 

 mixtures of solute crystals with the ice crystals) does not lie too 

 near the freezing point and whenever the substance is not excessively 

 toxic. He used strengths varying from -, to 2N of glucose and 

 glycerine, and -5- to 2N of methyl and ethyl alcohol, and mannite. 

 Of inorganic substances he used solutions with strengths of O.IN 

 to 2N of sodium chloride, potassium chloride, calcium chloride, 

 sodium nitrate, potassium nitrate, calcium nitrate, sodium acetate, 

 potassium acetate, calcium acetate, sodium lactate, potassium lac- 

 tate, sodium oxalate, and potassium oxalate, also magnesium nitrate, 

 magnesium chloride, ammonium nitrate, ammonium chloride, sodium 

 sulphate, and potassium sulphate. 



According to Maximow, mannite, sodium sulphate, potassium 

 sulphate, potassium nitrate, and sodium oxalate show little protec- 

 tion because of their high eutectic point; and magnesium chloride, 

 magnesium nitrate, and ammonium chloride because of their toxicity, 

 while calcium chloride and calcium nitrate show reduced protection 

 because of their toxicity. All other solutions, however, showed 

 great protection that was very uniform for the same osmotic con- 

 centration. Sometimes a temperature as low as -32 did not kill all 

 of the cells of the red cabbage. Probably the most interesting re- 

 sult of Maximow 's work was the observation that when the sections 

 were immersed in these solutions and immediately frozen, as much 

 protection was exerted as when they had been permitted to remain 

 in the solutions for twenty-four hours or longer. The tender Trad- 

 escantia cells immersed in expressed sap of the red cabbage and ini- 



'licr. der Doutach. Bot. GeseU.. Vol. 30. pp. 62-06, 203-306. 604-16. (HIbl. No. 73). 



