Ch. VIII, 3] VITALITY OP SEEDS 377 



Seeds apparently present no transformations into struc- 

 tures of other function, and few abnormalities or monstros- 

 ities. Tiie principal peculiarity of this kind consists in 

 POLYEMBRYONY (page 302), or the production of more than 

 one embryo to a seed. The additional embryos have di- 

 verse morphological origins, resulting oftenest from a budding 

 of nucellus cells into the embryo sac the structure taking 

 very perfectly the embryo form ; but they grow also from 

 other cells inside the embryo sacs, and from other embryo 

 sacs contained in the same nucellus. The embryos them- 

 selves often sliow a monstrosity in polycotyledony, the 

 production of cotyledons in more than the normal number. 



3. The Suspension of Vitality, Resting Period, and 

 Duration of Life in Seeds 



The primary seed function of serving as the disseminative 

 stage of the plant involves a number of physiological features, 

 of which the more prominent are indicated in the foregoing 

 title. 



The value, or necessity, of a suspension of vitality 

 during dissemination is qu'te obvious, since the embryo 

 plant while in transit, and hence for considerable periods of 

 time, is perforce exposed to great dryness, intense light, 

 destructive chemicals, etc. ; and these conditions are in- 

 consistent Avith that continuous interchange of oxygen, 

 water, and food essential to the ordinary life of plants. 

 As to the actual phj'sical method by which the suspension 

 of vitahty is insured in seeds, that seems to rest primarily 

 upon dryness, the greater part of the water being allowed 

 to escape without replacement during the ripening of the 

 seed. Since water is the indispensable solvent for chemical, 

 and the vehicle for physical, operations underlying growth and 

 other processes, its gradual withdrawal slows the processes 

 down, apparently evenly and without injury, until finally 

 a point is reached at which they are barely in action, — ■ 

 precisely as engines may be slowed, by withholding of power. 



