334 VEGETABLE PHYSIOLOGY 
setting up secondary injuries. The protoplasm becomes 
disorganised also at the low temperature. 
After the freezing of a tissue has taken place, a subse- 
quent rise of temperature leads to a process of thawing. 
This in many cases is more fatal to it than the freezing, but 
the effect depends largely on the rapidity of the thawing. 
If it is go gradual that the water can be re-absorbed into the 
cells, they may continue to live, but otherwise the organ is 
killed. The cells become flaccid and the protoplasm at 
once ceases to have the power of maintaining them in the 
turgid. condition. 
The effect of the absence of moisture in enabling vegetable 
organisms to resist cold has recently been examined in the 
case of seeds. Several kinds of these have been found to 
be capable of germinating after immersion for several hours 
in liquid hydrogen, the temperature of which is the lowest 
at present known. 
A similar effect is found at the other end of the scale. 
If seeds are heated very gradually some will withstand a 
temperature of 98° C. The gradual loss of water is a 
necessary condition for this immunity, for when the heat- 
ing is conducted so quickly that the water is not driven off 
at a low or moderate temperature, the treatment is fatal 
in all cases. Under conditions of gradual heating, their 
temperature being maintained at 60° C. for twenty-four 
hours, seeds have been found capable of germinating after 
a subsequent exposure to 98° C. lasting for ten hours. 
Spores of bacteria and of fungi have a great power of 
resisting high temperatures, and this is probably also asso- 
ciated with a considerable degree of dryness. They can 
withstand boilmg in water for some time, but it is probable 
that the reason why they are not destroyed ig that their 
walls successfully resist the passage of water into their 
interior. 
We are unable at present to explain in detail the causes 
of the death of protoplasm under the conditions of extremes 
of temperature. We can only say that under these con- 
