Germination. 27 



flay or loam, put 25 A'iable beans on tlie soil in each saucer, 

 then fill one saucer with moist sand and the other with 

 puddled clay or loam, pressing the latter down very 

 closely around the beans, cover both saucers with a bell- 

 jar, and xjlace in a warm room for two or three days, we 

 shall find that the l)eans co\'ered with the sand will 

 sprout promptly, while those covered with the puddled 

 soil will not (Fig. 4). In the sand-covered saucer the 



Fif^. -J. In the left haiijcl saucer beans wei'e planted in puddled soil. In 

 the other, tliey were covered with sand. They failed to germinate in the 

 puddled soil, because their contact with oxygen was cutoff. {From nature). 



air bet\A"een the grains of sand has had access to the 

 beans, while in the othei' the air has been shut out, which 

 explains the sprouting of one lot of seeds and the failure 

 of the other. About one-fifth of the atmosphere is free 

 oxygen, i. e., oxygen that is not chemically combined 

 with any other substance. 



AVe have seen that jprotoplasm in its active state re- 

 quires oxygen (13). Unless seeds are so planted that a 

 certain amount of this free oxygen can reach them they 

 cannot germinate.* Ordinary water contains a little free 

 oxygen, but not enough to enable many kinds of seeds 

 to germinate in it, though the seeds of some water plants, 

 as the water lily and rice will germinate in water. But 

 even these will not germinate in water that has been 



* This probably explains why very deeply-planted seeds rarely germi- 

 nate. 



