16 LAND DRAINAGE 



destruction takes place may be very rapid. The germs 

 have been known to destroy, in two weeks, enough nitrate 

 to produce a crop of wheat. 1 The process is called de- 

 nitrification, and the germs, denitrifiers. 



22. Ventilation and germination. The seeds of plants 

 cannot germinate in the absence of oxygen. Corn kept 



FIG. 4. The effects of ventilation on germination. The plant at the 

 right is taken from left jar, Fig. 3. The two kernels in the center 

 were taken from right jar, Fig. 3. They show absolutely no indica- 

 tions of germination. The kernel at the left was taken from a ger- 

 minator after 3 days. It shows the radicle making healthy growth. 



in a completely water-logged soil will never germinate. 

 If, before the vitality of the kernels is destroyed, the water 

 is removed from the soil and air permitted to come to the 

 kernels, they will germinate, but the vigor of the resulting 

 plant is likely to be impaired, perhaps seriously if the 

 germination has been much delayed. The partial exclu- 

 sion of air from seeds must retard germination, and often 



1 The writer has found that under water-logged conditions, 

 scarcely a trace of nitrates remained after 72 hours, where 

 originally large quantities existed. 



