Germination. 27 



of puddled* clay or loam, put 25 viable beans on the 

 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 place in a warm room for 

 two or three days, we shall find that the beans covered 

 with the sand will sprout promptly, while those covered 

 with the puddled soil will not (Fig. 4). In the sand- 



FIG. 4. In the left hand saucer beans were planted in puddled 

 soil. In the other, they were covered with sand. They failed to 

 germinate in the puddled soil, because their contact with oxygen 

 was cut off. (From nature.) 



covered saucer the air between the grains of sand has 

 had access to the beans, while in the other 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. 



"We have seen that protoplasm 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. f 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 



* Soil is said to be puddled when wet and packed until it is 

 in the consistency of putty. 



t This probably explains why very deeply-planted seeds rarely 

 germinate. 



