Notes . 
603 
doubt. That substances at widely extreme temperatures can remain 
in juxtaposition at least for some time, and still maintain them, is 
illustrated by a striking experiment shown by Professor Dewar at the 
Royal Institution on April 1, 1898. Liquid air poured into a large 
silver basin heated to redness, remained apparently as quiescent at 
this high temperature as in cooler vessels, and maintained a spheroidal 
condition. This is well understood. But the fact remains that liquid 
air with a temperature of about — 190° C. was contained in a vessel 
which had a temperature of 8oo° C-, the difference in temperature 
between the two being iooo°C. 
If we turn for a moment to the effect of heat on living structure, 
we know that a temperature of 75 0 C. is fatal to all protoplasm, 
because at that temperature its proteids are coagulated. Yet there is 
good evidence for the fact that seeds have been exposed for prolonged 
periods to a temperature above ioo°C., and yet have subsequently 
germinated. It may be taken as absolutely certain that in this case 
that temperature never reached the embryo, but must have been 
intercepted by the imperfect conducting power of the seed-coats. Cohn 
again has found that the spores of Bacillus subtilis survive prolonged 
boiling 1 , and a similar observation applies. 
It is probable that plant structures are deficient in thermal trans- 
parency, and they are notoriously indifferent conductors. Nevertheless, 
it is difficult to believe that in the case of such small bodies as seeds, 
their being brought to the temperature with which they are sur- 
rounded can be more than a question of time. 
That the thermal opacity of at least the seed-coats may be really 
considerable is not, however, impossible, even at low temperatures. 
The following remarks by Professor Dewar have an obvious bearing 
on this point : — 
‘Pictet, after an elaborate investigation, concluded that below a 
certain temperature all substances had practically the same thermal 
transparency, and that a non-conducting body became ineffective at 
low temperatures in shielding a vessel from the influx of heat. Ex- 
periments, however, prove that such is not the case, the transference 
of heat observed by Pictet appearing to be due not so much to the 
materials themselves as to the air contained in their interstices. 
Good exhaustion in the ordinary vacuum vessels used in low 
temperature work reduces the influx of heat to ene-fifth of what 
1 See Vines, Physiology of Plants, p. 283. 
