56 A MANUAL OF 



check. Wood ashes are, for the same reason, 

 one of the best fertilizers for all this class of 

 plants. Beautiful turnips and radishes may be 

 grown on a newly cleared fallow with scarcely 

 a tratce of the maggot. The great amount of 

 potash contained in the ashes is supposed to 

 be their most valuable element for this use, as) 

 this class of plants, and in fact all leguminous 

 plants, require a great amount of potash. 



Aside from its alkaline nature, lime has, in 

 our opinion, but little manurial value in itself. 

 Of course some of its constituents enter into 

 the structure of the plant, but its main use or 

 value as a manurial element consists in its 

 action upon the vegetable matter with which it 

 comes in contact, its tendency being to decom- 

 pose or set free the gases bound up in the vege- 

 table tissue, and render them available as plant 

 food. Therefore, when lime is used in combi- 

 nation with vegetable manure or with animal 

 excrement, the mixture should always be kept 

 under cover of the soil, that the gases may be 

 held from escaping until the plant absorbs 

 them. 



PLASTER OR GYPSUM is in its effects exactly 

 opposite to lime. It has a great affinity for 

 ammonia, phosphoric acid, and potash, and 



