Sunlight upon Aquatic Plants. 375 
does not apparently begin to freeze until the temperature 
approaches or falls below — io° C. The water occupying the 
centre of the micellar canals or interstices of an organized 
structure will be the first to freeze. The film of water or 
layer of water-molecules directly abutting upon the walls of 
the micellar canals and coming within the sphere of the 
molecular influences radiating from the molecules, molecular 
complexes, or micellae composing these walls, will be re- 
strained with even greater force from assuming the molecular 
arrangement and character constituting the solid condition. 
The amount of such water is, however, relatively trifling, and 
being firmly retained can hardly be made use of in metabolism 
when no other supply of water is available. It is possible, 
therefore, to make the dogmatic statement that no manifesta- 
tion of vital activity can take place at a temperature below 
— 10 C. to — i2°C. Jumelle has already been shown to be 
in error in supposing that C 0 2 -assimilation could continue 
at temperatures as low as — 30° C. to — 40° C. 1 It is, 
however, in all cases safe to conclude that plants which can 
withstand complete desiccation cannot be killed by cold. 
This has been shown to be the case with several of the more 
resistant Bacteria and bacterial spores by the researches of 
Dewar and McKendrick, as well as by other investigators, 
while Chodat 2 has shown that the spores of Mucor mucedo 
survive exposure to from — 70° C. to — no° C. for two hours 3 . 
Similarly many Palmellaceae, Cyanophyceae, &c., can with- 
stand prolonged desiccation over sulphuric acid, and, as has 
already been shown, complete freezing also, even when in 
the vegetative condition. Such are Haematococcus pluvialis , 
Pleurococcus vulgaris , Pleurococcus miniatus , Rhaphidium 
polymorphum , Gloeocapsa , Merispomedia , Nos toe commune , 
Oscillaria antliaria , O. tenuis and O. subfusca . On the other 
hand, Confervae, Haematococcus nivalis , the zoospores of 
1 See Assirn. Inhib., 1 . c., p. 402. 
2 Chodat, Bulletin Herb. Boissier, 1896, p. 870. 
3 Brown and Escombe subjected a variety of air-dried seeds to a temperature of 
-183° C. to -192 0 C.for no hours, and found that their germinative power was not 
perceptibly affected. (Proc. Roy. Soc., lxii, 1897, p. 160.) 
C c 3 
