18 



LAND DRAINAGE 



of oxygen is restricted, the growth of roots is retarded 

 and the crops suffer. 



24. Removal of objectionable products. All growth 

 results in the production of carbon dioxide. Animals 

 throw this gas from their lungs into the air. The roots 



FIG. 6. Effects of ventilation on germination. Same as Fig. 3, 14 

 days from planting ; 7 days after water was removed from right jar. 

 Seventy per cent only of the kernels have germinated. 



of plants and the lower plant forms growing in the soil 

 produce carbon dioxide (CO 2 ) and liberate it in the soil. 

 The presence of carbon dioxide (CO 2 ) interferes with the 

 life in the soil, as does its presence with animal life in a 

 room. When, therefore, there is an unbalanced condi- 

 tion of air in the soil, too little oxygen, too much car- 

 bon dioxide, the balance must be reestablished before 

 plant life can thrive. 



