GEKMINATION. 353 



6. Moisture. — A certaia amount of moisture is indis- 

 pensable to all growth. In germination it is needful 

 that the seed should absorb water so that motion of the 

 contents of the germ-cells can take place. Until the 

 seed is more or less imbued with moisture, no signs of 

 sprouting are manifested, and if a half-sprouted seed 

 be allowed to dry the process of growth is effectually 

 checked. 



The degree of moisture different seeds will endure or 

 require is exceedingly Tarious. The seeds of aquatic 

 plants naturally germinate when immersed in water. 

 The seeds of most agricultural plants, indeed, wjll 

 quicken under water, but they germinate most health- 

 fully when moist but not wet. Excess of water often 

 causes seeds to rot. 



c. Oxygen Gas. — Free Oxygen, as contained in the 

 air, is likewise essential. Saussure demonstrated by ex- 

 periment that proper germination is impossible in its 

 absence, and cannot proceed in an atmosphere of other 

 gases. The chemical activity of oxygen appears to be 

 the means of exciting the growth of the embryo. 



d. Light — It has been erroneously taught that ligTit 

 is prejudicial to germination, and that therefore seed 

 must be covered. {Johnston's Lectures on Ag. Chem. & 

 Geology, 2d Eng. Ed., pp 226 and 227.) Nature does 

 not bury seeds, but scatters them on the surface of the 

 ground of forest and prairie,, where they are, at the most, 

 half-covered and by no means removed from the light. 

 The warm and moist forests of tropical regions, which, 

 though shaded, are by no means dark, are covered with 

 sprouting seeds. The seeds of heaths, calceolarias, and 

 some other ornamental plants,^ germinate best when un- 

 covered, and the seeds of common agricultural plants 

 will sprout when placed on moist sand or sawdust, with 

 apparently no less certainty than when buried out of 

 sight. 



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