150 ADMISSION OF THE AIR. 



cultivation, as in the diagram before, when the 

 porous substratum crops out ; but where a stratum 

 underlies the surface-soil at a regular depth it can 

 only be incorporated with it by deep ploughing or 

 digging. 



4. The atmosphere is admitted to the roots, and 

 consequently the fertility increased by deep cultiva- 

 tion. When a boy, I discovered a hole in which a 

 woodchuck had residence, and commenced to dig 

 him out of his intrenchment. The space dug over 

 was about eight feet square and two feet deep. A 

 handful of grass-seed was scattered upon the spot, 

 that our sport might not injure the mowing the 

 next year, and very little hay was expected ; but it 

 so far eclipsed the surrounding fields in the luxuri- 

 ance and quality of its crop, that the whole field 

 was treated in the same manner. This result must 

 have been attained through admission of air to the 

 soil, as no manure was applied. Prof. C. W. John- 

 son says M. Saussure has shown how essential a 

 free access of air is to the roots of plants. He 

 " found that oxygen gas was absorbed by the roots 

 as well as by the leaves, and that it is there united 

 with carbon, and transmitted to the leaves to be 

 decomposed. It has been proved that vegetation is 

 greatly increased by nourishing it with water im- 

 pregnated with oxygen gas ; hence, too, the superi- 

 ority of rain-water. Some recent experiments were 

 ^made by Mr. Hill, demonstrating the great benefit 



