366 Ewart . — The Action of Cold and of 
some time. That Spirogyra is very sensitive to cold is 
quite certain. Thus a sample of class-material composed 
of vS. crassa and S'. nitida was killed in a single night, 
owing to the temperature accidentally being allowed to fall 
from about 20° C. to just below zero, and that although no 
actual ice-crystals were formed in the water in which the 
plants lay. Similarly with actively vegetating specimens of 
Spirogyra nitida , S. crassa , S. flavescens , Vaucheria sessilis ) 
V. terrestris , and of Nitella , all the vegetative parts were 
killed by exposure during a single night to a temperature 
not falling below — 2° to — 3°C., which caused a partial con- 
version only of the surrounding water into ice. After freezing 
for one night at from — 2° C. to — 5 0 C., Vallisneria spiralis , 
Cladophora , and Chara were entirely killed ; in Elodea cana- 
densis occasional living cells were still to be found ; Lemna 
minor and Lemna trisidca were partially killed ; while of 
Diatoms and Desmids, very many of the Desmids Euastrum 
and Closterinm were killed, and many of the Diatoms 
Navicula and Pinnularia. After being frozen at — 8° C. to 
— io°C. for several hours by means of a freezing mixture of 
ice and salt, Lemna minor and L,emna trisidca were killed, 
as well as both the Diatoms and Desmids. In the former, 
as is usually the case, the chlorophyll bodies were broken up 
and disorganized. In the latter the ‘ Endochrome } was also 
disorganized and frequently shrunken, while no plasmolys- 
ability could be detected in any of the cells. When, however, 
the cultures were returned to normal conditions, after two 
weeks or so, living Diatoms of the same kind reappeared, 
but no Desmids. In the former case apparently a few 
resistant forms had remained living and escaped observation. 
This might possibly have occurred with the Desmids also 
had these previously formed any resistant spores. 
Of several Oscillarias examined, all remained living, though 
in some cases the filaments were in part killed. Similarly 
in Gloeocapsa , Scenedesmus , and Protococcus most or almost 
all of the cells remained living, whereas the zoospores of 
Protococcus ( Chlamydococcus ?) were dead and non-motile when 
