68 SEEDS AND FRUITS 



in the seed by allowing tlie greater part of the water to escape 

 during the process of maturing. Since the hfe 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 long 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 hquid 

 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. 



