259 



The theory of the impossibility for an organism to 

 freeze as long' as it is alive was still accepted some fifty 

 years ago since Miiller-Thurgau (1886) deemed it neces- 

 sary to point out that his own experiments, in which 

 plants were found alive after freezing and thawing, spoke 

 against such a view. 



There is some resemblance between this apparently 

 antiquated theory and some modern forms of the "bound 

 water" hypothesis, according to which living matter 

 would bind a certain quantity of M^ater in such a way that 

 the crystallization forces would have to tear away this 

 water and, in doing so, kill the protoplasm, before freez- 

 ing can occur. 



II. THEORY ATTRIBUTING DEATH TO THE ATTAIN- 

 MENT OF A MINIMAL TEMPERATURE 



The theory that death is due to the removal of a given 

 quantity of energy leads naturally to the idea that there 

 is a definite death temperature for each species of ani- 

 mal or plant. In this form, the theory has been known 

 as that of the "specific minimum". It was developed 

 mostly by Mez (1905) and his pupils Apelt (1907), Rein 

 (1908) and Voigtlander (1909). 



Mez (1905), considering that some plants are killed 

 by cold at temperatures above zero while others resist 

 hard freezing, and that some seeds present a high cold 

 resistance (Avena, Triticum) while others are rather 

 sensitive to cold {Lobelia), developed the theory that for 

 each plant species there is a temperature minimum be- 

 low which the plant cannot live. This minimum, or death 

 point would be characteristic of each species, under a 

 given set of conditions, such as, water content, age, stage 

 of development, etc., but it would change when any one 

 of these conditions changes. Drying, for example, would 

 lower the specific minimum. The development of a seed 

 into embryonic tissues would raise the minimum. 



