362 Vegetation and Frost. 
maintained at about that amount. This we should consider as the 
result of the accumulation of the products of diastatic hydrolysis 
of starch hindering the further progress of the reaction (to speak 
statically). That the limit attained depends on the concentration 
of the sugar Muller showed by cooling potatoes which had been 
caused first to lose a lot of water by slow drying. These potatoes 
formed sugar to about the same concentration, and therefore to a 
less absolute amount than watery turgid tubers. 
If potatoes are hept at +3° the sugar content does not rise 
above •5 %, while at +6"C hardly a trace of sugar is to be found. This 
phenomenon is then essentially a disturbance of metabolic balance 
due to low temperature. The amount of sugar at any moment 
depends partly on the diastatic activity and partly on the con¬ 
sumption of the sugar in respiration. As the temperature falls, 
the respiration will be much diminished, and this favours the accumu¬ 
lation of sugar. Diastatic activity is also diminished by cold, but 
the equilibrium point finally attained between starch and sugar is 
shifted towards the sugar by cold. Equilibrium points of reversible 
reactions are always shifted with fall of temperature in the direction 
of a greater concentration of the products of the exothermic 
direction of the reaction ; that is, in this case, a greater con¬ 
centration of sugar. 
On warming a sugary potatoe to 20 n C the sugar rapidly dis¬ 
appears, an increased portion of it is respired, and the rest recon¬ 
verted to starch by another shifting of the equilibrium point, now 
in the opposite direction. We must not follow Muller’s attempt to 
consider these factors quantitatively, but it is of interest that the 
balance of starch and sugar in these living cells of tubers, tree- 
trunks or winter-green leaves alters with temperature according to 
an established thermo dynamical law. We cannot yet say to what 
extent physiological processes or biological adaptations are super¬ 
posed upon this fundamental principle to produce so great an accu¬ 
mulation as to act as a satisfactory protection against winter frost. 
F. F. BLACKMAN. 
LITERATURE. 
H. Muller-Thut'gau. “ Uber das Gefrieren und Erfrieren der Pflanzen.” 
Theil I., Landwirthscliaftliche Jahrbiicher. Bd. IX. 
1880. Theil II., ibid, Bd. XV., 1886. 
,, . M “ Uber Zuckeranhiiufung in Pflanzentheilen in Folge 
niederer Temperatur.” ibid, Bd. XL, 1882. 
H. Molisch. “ Untersuchungen iiber das Erfrieren der Pflanzen.” Jena, 1897. 
