362 
PHYSIOLOGY. 
BOOK II. 
apparently suffer, by being exposed for a quarter of an hour 
to a temperature equal to freezing mercury: such grains 
were afterwards placed in a proper situation, and germi- 
nation took place as usual. Considering that the particles of 
faecula of which seeds consist are not liable to bursting 
below a temperature of 75° centig. (167° Fahr.), these ob- 
servers were led to ascertain how near an approach to this 
extreme temperature might be made, without destroying 
vegetable life. Seeds of various cereal and leguminous 
plants were placed for a quarter of an hour in water of this 
temperature, and they were all killed ; five minutes were 
afterwards ascertained to suffice for the destruction of three 
in five. Less elevated temperatures were next experimented 
on. Wheat, Barley, Kidneybeans, and Flax were killed in 
minutes, by water at 62° centig. (143*6° Fahr.) ; a few 
grains of Rye and some Beans required a longer exposure 
to be destroyed. When the temperature was lowered to 
52° centig. (125*6° Fahr.), most of the seeds in experiment 
retained their vitality ; but even this was fatal to Barley, 
Kidneybeans, and Flax. 
Fluid water has conducting powers very different from 
those of vapour or of dry air ; it was thereupon important, 
to determine whether the temperature that seeds can bear 
is regulated by the nature of the medium in which they are 
exposed to it. In vapour, 75° centig. (167° Fahr.) was suffi- 
cient to destroy such seeds as were exposed ; but, at 62° centig. 
(143*6° Fahr.), they retained their vitality, after having been 
under experiment for a quarter of an hour. But, in dry air, 
many seeds bore the temperature of 75° centig. (167° Fahr.), 
for a quarter of an hour, without inconvenience. Hence it 
appears that seeds in steam can bear 12° centig. more than 
in water, and in dry air 13° centig. more than in steam. 
In these experiments, the action of temperature w^as ex- 
tremely rapid. In lowering the temperature and prolonging 
its action, it was found that, when Wheat, Rye, and Barley 
were exposed for three days, in water, to a temperature of 
35° centig. (95° Fahr.), four fifths of the Wheat and Rye, 
and all the Barley, were killed. Hence it would appear, 
that 35° centig. forms the highest limit of temperature which 
