462 



THE SEED AND ITS GERMINATION. 



GERMINATION. 



1199. Germination, 1 the process by which an embryo unfolds 

 its parts, is complete when the plantlet can lead an independent 

 existence. 



1200. The conditions necessary for germination are (1) moist- 

 ure, (2) free oxygen, (3) warmth. 



1201. The amount of water required to initiate the process 

 of germination is, in general, that which will completely saturate 

 and soften the seed. Germination does, however, begin in cer- 

 tain cases even when only the radicle and the albumen directly 

 around it have become soaked. 



The amount of water requisite for the saturation of a seed has 

 been determined for a large number of plants, and will be seen 

 by a comparison of the results to vary within wide limits, depend- 

 ing on the percentage of water already present and the character 

 of the albumen. It is plain that in very exact determinations 

 account must be taken of the possibility of a loss by the seed 

 of a portion of its contents while in water ; in three days this 

 amounts in the common bean to a little over two per cent. The 

 cereals require a comparativel}' small amount of water for satu- 

 ration, while leguminous seeds absorb a much larger quantity. 2 



1 It is well to distinguish between two stages in the process of germination, 

 (1) that marked by the protrusion of the first rootlet, (2) the subsequent de- 

 velopment of the embryo into an independent plant. The reason for making 

 this distinction is, that most of the experiments upon the relations of tempera- 

 ture, etc., to germination have usually terminated at the first stage ; whereas 

 the vigor of the plantlet as seen at a later stage is an important factor in 

 deducing results to guide practice in sowing seeds. 



2 The table below, by Hoffmann (Vereuchs-Stationen, vii., 1865, p. 52), has a 

 parallel column of results obtained at Tharandt (Nobbe: Samenkunde, p. 119): 



