Frost and Vegetation. 361 
This brings us to Lidforss’ theory of the protective action 
of sugar. It is simply this, that the presence of sugar retards the 
salting-out effect investigated by Gorke. Spiro had found that the 
presence of non-electrolytes, like alcohol, glycerine, sugars, etc., 
hinders the coagulation of proteids, and that indeed the presence 
of sugar may raise the heat-coagulation point of a given proteid 
from 59 n C to 85°C. 
Lidforss found by experiment that the addition of 5% to a 
mixture of egg-albumen and dilute Knop’s nutritive salt-solution 
much diminished the amount of proteid precipitate that ensued on 
freezing, and that 10% sugar prevented altogether such pre¬ 
cipitation. 
Combining this with Gorke’s experiments on freezing whole 
plants and actual expressed sap, it seems safe to transfer these 
effects observed in vitro to the living cell, and to accept this 
theory that the universal formation of sugar in winter-leaves acts 
as a distinct protection against winter cold. 
To prevent our deriving too great satisfaction from this 
interesting chain of reasoning, we may recall that two charac¬ 
teristic sugar-plants, the sugar-cane and the sugar-beet arc both 
very susceptible to cold and that sugarless Bacteria on the contrary 
are very resistant. Of course the constitution or composition of 
the protoplasm will have the final word in this matter. 
We may now attempt to carry our enquiry a stage further and 
ask how it comes about that winter-leaves convert their starch to 
sugar. 
This phenomenon is not confined to leaves, but Russow and 
Fischer found that in most trees the periderm of the trunk contains 
sugar and oil in winter, in place of the starch present in summer. 
Potato tubers too kept at temperatures near zero are well 
known to turn sweet and unpalatable This interesting phenomenon 
was worked at with great insight and precision by Muller-Thurgau 
as long ago as 1882. He first shewed that sugar formation was 
not the result of injury by frost and that indeed it does not take 
place when the tuber is kept frozen hard, below —1°C. At 0"C 
the conversion of starch to sugar proceeds steadily, and potatoes 
stored upon ice may go on accumulating sugar for forty or fifty 
days. The accumulation begins slowly, and then proceeds faster 
and faster for a time, till it reaches somewhere about 3% of the 
fresh weight. Then the increase stops and the sugar content is 
