( 81 ) 

 caustic, readily becomes carbonated under 

 the influence of the carbonic acid of the atmos- 

 phere and of the moisture of the soil, it is bet- 

 ter to hasten this neutralization (in order to 

 preserve the plants from the action of the 

 caustic lime,) by distributing it over the sur- 

 face as uniformly as possible. 



Marl. Marl owes its power as a manure 

 to its calcareous matter, and marling therefore 

 isanalagous to liming. Argillaceous marl acts 

 by reason of both its lime and clay, and hence 

 is very appropriate for sandy soils where the 

 clay, it contains, acts mechanically. Very 

 probably, marl may also operate as a nitroge- 

 nous manure, as Payen and Boussingault have 

 found organic matter in many marly sub- 

 stances. 



As the plants remove the lime from the 

 soil, it is evident that the action of one marl- 

 ing is not illimitable. Three and a half bush- 

 els are the usual proportion, and, by compa- 

 ring its composition with that of the plants^ 

 it will be readily seen that this amount is suf- 

 ficient 



Wood ashes. Notwithstanding the good 

 efifects of this manure, it is but little used in 

 agriculture, because of its great value as mate- 



