CH. II.] THE ROOT. 91 



nivorous is the most prompt in benefiting vegeta- 

 tion : witness night soil, pigs' dung, &c. ; but such 

 manures are not the most permanent. Hassenfratz 

 manured two portions of the same soil, No. 1 with 

 a mixture of dung and straw highly putrefied ; 

 No. '2, with a similar mixture, newly made. He 

 observed that during the first year the plants in 

 Xo. 1 produced the best crop, but the second and 

 third years (no more dung being added) No. Q, pro- 

 duced the best crop ; after which, both seemed alike 

 exhausted^. The same chemist found, that a soil 

 manured with wood-shavings did not, dui'ing the two 

 succeeding years, produce a superior vegetation to 

 the same soil without any manure ; the third year, 

 however, it was better, but it was not mitil the filth 

 year that it reached the maximum of fertility. The 

 site of a wood stack, and the newly cleared lands of 

 America are eminently fertile, from the gradually 

 decomposing vegetable remains they contain. 



These facts and obsen^ations teach us that the 

 most prompt manures are the reverse of economical. 

 Vegetable remains, incorporated with a soil, will 

 insure an average produce dming several years; 

 animal matters and dungs highly putrescent are 

 powerfully but transiently beneficial. Putrefaction 

 is evidently the means of rendering these substances 

 available to plants : hence, thoroughly decayed stable 

 * Ann. de Chimie, xiv. 57. 



