I2O 



SOILS AND FERTILIZERS 



experiments, but in a different way. The plants were 

 now grown in a large carboy with a limited volume of 

 air so as to cut off all sources of com- 

 bined nitrogen, as traces of ammonia, 

 nitrates, and nitrites. By means of 

 a second glass vessel (B, Fig. 30) the 

 carboy was kept liberally supplied 

 with carbon dioxide, so that plant 

 growth would not be checked for 

 lack of this material. When experi- 

 ments were carried on in this way, 

 using a fertile soil, the plants reached 

 full maturity ; but when a soil free 

 FIG. 30. Plants grown from nitrogen was used, plant growth 

 m carboy. wag SQQn c h ec k e d. A general sum- 



mary of this work is given in the following table : ^ 



NITROGEN 



These experiments show that with a sterilized soil, 

 and all sources of combined atmospheric nitrogen cut 

 off, the free nitrogen of the air takes no part in the food 

 supply of the plant. 



