Soils for Vegetable-Gardening in Warm Countries 3 



When soil contains an easily perceptible amount of 

 carbonate of lime, it is said to be calcareous or marly. 



When a very large percentage of vegetable matter is 

 present, the soil is usually called muck or vegetable mold. 



COMPOSITION OF SOILS 



Soils that are in good condition for raising crops are made 

 up of about fourteen elements. There are more elements 

 that may occur in soils; but as only about thirteen of 

 these are actually used by plants, we need not regard the 

 others, with the exception of aluminium, which, although 

 not a plant-food, yet is the chief constituent of all clays. 



Elements necessary for plant growth. 



The essential elements for plant growth are oxygen, 

 hydrogen, nitrogen, carbon, sulfur, phosphorus, potassium, 

 calcium, magnesium, and iron, together with sodium, 

 silicon, and chlorin. Oxygen, hydrogen, and carbon are 

 mainly, and nitrogen partly, derived from the air. They 

 constitute 95 to 99 per cent of the weight of plants. 

 While these four elements are derived from the air, it 

 should not be understood that they are usually taken 

 directly from it by the plant, nor do they usually enter 

 the plant in the condition of a simple element. All parts 

 of plants, however, take oxygen from the air as they re- 

 spire, and some plants, belonging to the pea family, are 

 able, under certain conditions, to assimilate more or less 

 nitrogen indirectly from the air. Because the above- 

 named four elements make up so much of the weight of 

 plants, it should not be inferred that the other nine ele- 



