20 



CHAPTER IT. 



ON SOILS AND MANURES ; INCLUDING THE 

 FORMATION OF HOTBEDS. 



The art of cultivating hardy plants consists in 

 improving their size or quality, by giving them 

 more food than they could have obtained in a 

 state of nature ; but the plants of hot countries, 

 when they are to be grown in a cold climate, 

 require in addition artificial heat and shelter. 



To know how to supply plants with food, we 

 must remember that they are organised beings, 

 composed principally of carbon, oxygen, hy- 

 drogen, and nitrogen ; and that they require a 

 constant supply of these elements to enable 

 them to live and grow. They also require cer- 

 tain mineral or earthy substances, which differ 

 according to the nature of the plant. The 

 elementary substances required for the nourish- 

 ment of plants are derived partly from air and 

 water, partly from the soil, and partly from 

 substances occasionally added to the soil, which 

 are called manures. Manures are also used to 

 create artificial heat. 



Carbonic acid gas and nitrogen gas are found 

 in the atmosphere ; and the plant possesses the 

 power of absorbing them by its roots, as well 

 as its leaves, if air be permitted to have access 

 to its spongioles. The plant takes up oxygen 



