130 NATURE TEACHING. 



amount of the material disappears, and that a 

 comparatively small amount of ash remains. 

 This ash is the mineral matter of the plant, 

 the carbon and nitrogenous substances hav- 

 ing burnt away. 



EXPERIMENTS WITH MANURES. 



1. By cultivating plants in boxes or in 

 isolated garden plots, experiments may be 

 made as to the action of the various manures 

 in common use. The soil of an ordinary 

 garden is usually fairly well supplied w.ith all 

 the necessary constituents of plant food. In 

 order therefore to obtain immediate, and 

 striking proof of the effects of manures it is 

 advisable to use poor soil. Sand is very con- 

 venient and, if obtainable, should be employed. 

 In most localities accumulations of sand, suita- 

 ble for the purpose, can be found, for instance 

 on the sea beach or in beds of streams. The 

 sand used should be free from salt, vegetable 

 matter (humus), or other plant food. Before 

 using it, therefore, it is advisable to wash it 

 thoroughly to remove the salt. The manner of 

 doing this will depend on the facilities at hand. 

 A convenient method is to put the sand into a 

 barrel, the bottom of which has a number of 

 holes bored in it, and to pour water on it. The 

 water will drain away through the holes, and 



