ay 
this as a regular thing, blossoming each year in midsummer. It 
is hardly necessary to add, however, that repeated injury like this 
cannot be for the best good of the plant. Further, the rank 
growth put forth by killed back individuals 1s the more sensitive 
to injury the succeeding winter. 
Nature of Injury from Extreme Cold 
Sachs long ago showed that under ordinary conditions, when 
plants are frozen, water passes out from the protoplasm and 
freezes in the intercellular spaces. When thawing occurs, the 
resultant water remains in the intercellular spaces until it is either 
evaporated or is reabsorbed by the cells which had released it, and 
which had become more or less plasmolyzed. In some cases it 
requires considerable time for the protoplasm to resume its normal 
condition and position and thus for the cell to regain its turgidity. 
Freezing in plants has been observed by Wiegand ! to occur in the 
intercellular spaces. Water withdrawn from the cells forms ice 
crystals in these spaces. [Excessive withdrawal of water from the 
cells of course results in considerable plasmolysis, and if this con- 
tinues to an extreme point, death must ensue. It seems obvious 
that continued or extreme low temperatures would cause a con- 
tinued removal of water from the cell, thus eventually causing 
the death of the cell itself. 
Winter Injury the Result of a Complex of Conditions 
Although we believe that the extreme low temperatures of the 
past winter were the fundamental cause of the injuries to our 
woody plants, yet it is evident, after careful observation of the 
different plants, that the matter is not really so simple as this. 
No one can gainsay the fact that, given sufficiently low tem- 
perature, protoplasm will freeze, or at least become so altered 
chemically that it is no longer protoplasm, and hence no longer 
alive. Yet the physiological condition in which the plant finds 
itself at the onset of the cold period has much to do with its relative 
susceptibility and the extent of injury it sustains. This explains 
1 Wiegand, K. M. The passage of water from the plant cell during 
freezing. Plant World 9: 107-118. 1906. 
