THE PRINCIPLES OF BOTANY. 
399 
weeks in coming up, while barley sown in warm weather was 
up in four warm days. 
Seeds are, however, very variable in this respect, for 
whereas mustard and cress will germinate in a few hours, 
the Haws of the white thorn and some of the seeds of sloe 
fruits will take from one to two years. 
In practice we find that all seeds will germinate more 
readily by being soaked in water previous to sowing. 
The temperature at which seeds germinate has formed a 
subject of inquiry by several observers. If the temperature 
be too low seeds cannot germinate at all, and if too high 
they grow so fast as to become weak and spindly ; it is, there¬ 
fore, a point between these extremes that will be best suited 
to plants, and this point would seem to vary with the indi¬ 
vidual specimens. 
Edwards and Colin found that wheat, barley, and rye 
could germinate at 7° centigrade (44'6° Fahr.), and that 
grain of the same description did not 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 germination took place as 
usual. Considering that particles of fsecula of which seeds 
consist are not liable to bursting below a temperature of 
75° centigrade (167° Fahr.), these observers 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 w^ater 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, 
kidney beans, and flax, were killed in twenty-seven minutes 
and a half by water, at 62° centigrade (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° centigrade (125'6° Fahr.), most of the seeds in expe¬ 
riment retained their vitality, but even this was fatal to barley, 
kidney beans, and flax.* 
The disruption or softening of the external tissues or 
coverings of seeds greatly aids the process of decomposition 
of seed, which is the prime element in their digestion; and, 
indeed, without this, either by cooking or bruising, seeds can 
pass through the stomach of animals without having their 
vitality impaired. Hence, as a matter of economy, corn 
* See Lindley’s ‘Introduction to Botany,’ vol. ii, p. 262. 
