498 
J. G. GROSSENBACHER 
and even applies his low-temperature tension hypothesis to cold 
injury of herbaceous plants. 
Some interesting advances have been made in recent years in the 
study of the chemical and physiological side of this question, but 
unfortunately the investigators interested in this phase of the subject 
have thus far given no attention to the more simple physical con- 
comitants presented by Sorauer in the papers just referred to. It is 
in fact usually assumed that the earlier works had decided this matter. 
Nageli,^^ for example, made some studies of this type and concluded 
that since walls of Spirogyra cells killed by low temperature are not 
ruptured, death must be due to changes induced in the protoplasm. 
Kunisch^^ maintained that low temperatures induce harmful irre- 
versible changes in certain components of the protoplasm that result 
in the death of tissues; that in some plants such changes may even 
occur above the freezing point, although in others a temperature 
much below freezing is necessary to cause injurious effects. Fischer, 
after very fully discussing the literature and giving the results of his 
own extensive experimental study of the problem, concluded that the 
low-temperature death-point of plants usually does not vary more than 
two, though it may vary as much as ten, degrees. On the other 
hand, Winkler^^ found that the condition of the protoplasm at the 
time of the occurrence of the low temperature has much to do with 
the degree of resistance or injury. 
Some have held that low-temperature injury results from ice- 
formation; others believe that it is the withdrawal of water during 
freezing that causes the injury. Apelt and others^^ have brought 
, liber Frostschorf an Apfel- und Birnenstammen, Zeit. Pflanzenkr. i: 137. 
1891. 
Nageli, C, Ueber die Wirkung des Frostes auf die Pflanzenzellen, Sitzungsb. 
Akad. Wiss. Miinchen i: 264. 1861. 
Kunisch, E. H,, Ueber die totliche Einwirkung niederer Temperaturen auf 
die Pflanzen, Inaug. Dissert. Breslau. 1880. 
Molisch, H., Untersuchungen iiber das Erfrieren der Pflanzen. Jena. i89>. 
, Das Erfrieren von Pflanzen bei Temperaturen iiber dem Eispunkt, 
Sitzungsb. Akad. Wiss. Math. Naturw. (Wien) 105: 82, 1896. 
^"^ Fischer, H. W., Gefrieren und Erfrieren, eine physico-chemische Studie, 
Beitr. Biol. Pflanz. 10: 133. 191 1. 
1^ Winkler, A., Uber den Einfluss der Aussenbedingungen auf die Kalteresistenz 
ausdauernder Gewachse, Jahrb. Wiss. Bot. 52: 467. 1913. 
13 Miiller-Thurgau, H., Ueber das Gefrieren und Erfrieren der Pflanzen, Landw. 
Jahrb. 9: 133. 1880. 
