8 PLANT PHYSIOLOGY 



cell cease with the demolition of its structure. Dehydration 

 is fatal to nearly all plants and their parts, rapid dehydra- 

 tion is fatal to all; but ripe seeds, in which all the vital 

 activities are greatly reduced as the embryo attains the 

 stage of development characteristic of the species, can with- 

 out injury slowly give up nearly all the water which they 

 contain. By this means the protoplasmic structure, the 

 arrangement of the protoplasmic particles, necessary to 

 active life, is sufficiently altered to cause an entire suspen- 

 sion of all activities. In a climate of average humidity 

 water will still remain in air-dry and wholly dormant 

 seeds, as may be shown by weighing them air-dry and re- 

 weighing after they have been dried for an hour in an oven 

 at a temperature of 70 C., or for a longer time at room 

 temperature in a desiccator. The following table, quoted 

 from Schroder,* shows the percentage cf water contained 

 in ripe and air-dry grass " seeds," thus 



Hordeum vulgare, 14.65% 

 Triticum durum, 14.63% 

 Triticum spelta, 14.40% 



This amount, though considerable, is less than the con- 

 stitutional water of the active protoplasmic structure, and 

 hence all vital activity is extremely slight. With the restora- 

 tion of the water of constitution, and after the lapse of a 

 part if not all of the usual "resting period' 7 of the seeds, 

 the vital functions will be resumed. 



The spores of many of the lower plants are also able to 

 bear the withdrawal of the water of constitution without 

 permanent injury, and like seeds, they can withstand during 

 this period of inaction degrees of heat and cold, amounts 

 of poisonous gases, and other influences which at other 

 times would be fatal to them. The dry seeds of peas and 

 beans, the grains, etc., and the dry spores of various fungi, 

 can be subjected for hours to a temperature of about 100 

 C. without destroying their germinating power, although 

 about half that temperature would in fifteen minutes be 



* Untersuchungen aus dem Botan. Institut zu Tubingen, Bd. II., p. 10, 



1886. 



