68 SEEDS AND FRUITS 
in the seed by allowing the greater part of the water to escape 
during the process of maturing. Since the life processes depend 
upon water for dissolving and transporting the necessary sub- 
stances, they are naturally slowed down when water is with- 
drawn and apparently without injury even when so checked 
that no action can be detected by ordinary laboratory methods. 
Some investigators have maintained that these life processes 
actually stop, but the evidence sustains the view that these 
processes never stop so Jong as the seed remains capable of ger- 
minating. There are various factors involved in maintaining the 
rest period, but chiefly they have to do with keeping water and 
oxygen from the embryo. 
The ability of seeds to endure extreme conditions while in the 
resting stage is well shown in the case of temperature. In liquid 
air, seeds of Alfalfa, Mustard, and Wheat have been kept at a 
temperature of —250° C. for three days and afterwards success- 
fully germinated, though their embryos when active are quickly 
killed by a temperature a little below freezing. The ability of 
dry seeds to endure heat is also surprising. Some in the resting 
stage, if kept dry, can endure a temperature of 100° C., the tem- 
perature of boiling water, without having their vitality impaired, 
while their embryos, if active, would perish at 60° C. 
The length of the resting period varies much for different kinds 
of seeds and for seeds of the same kind. In a sample of Clover 
seed, for example, many of the seeds may germinate in two or 
three days, and some may not germinate for a month or a year. 
Although the seeds of some wild plants will germinate as soon as 
mature, if given favorable conditions of moisture and warmth, 
most of them, however, have a rest period which extends over 
days, weeks, months, or even years, and often saves the young 
plants from getting started at a time when they would soon be 
caught by unfavorable conditions. Excepting some seeds like 
those of the Clovers and Alfalfa, the seeds of cultivated plants will 
usually germinate about as soon as mature. Although a desirable 
feature, it sometimes results in loss, in that Corn, Wheat, Oats, 
and other crops germinate in the field if the weather following 
harvest is warm and wet. The resting period, which is retained 
by Wild Oats and some other wild plants kindred to cultivated 
ones, has been lost from our cultivated plants through many 
years of selection. 
