34 INTRODUCTION. 



and precipitated when the current is in a certain 

 degree moderated. It is found of many different 

 colours ; contains but little vegetable food ; but 

 is an indispensable component in all composts. 

 The pure white, or lightest coloured, usually 

 found on commons, is the best for the florists 

 and all horticultural purposes : the deep-brown 

 or black, often containing ferruginous qualities, 

 is hurtful to most plants. Sea or river sand 

 may sometimes be used with propriety and ad- 

 vantage when pure pit sand cannot be had. 



Clay — In its general character, is composed 

 of very minute particles of earth reduced to their 

 ultimate degree of fineness ; consequently closely 

 compacted, adhesive, impervious to air or water; 

 hardens in the sun, and burns to a red earth. 

 Clay is changed into loam by cultivation, and 

 the addition of sand, lime, and other friable sub- 

 stances. 



Loam. — Soils, commonly so called, are supe- 

 rior to all other for the purposes of the florist. 

 It is a well-proportioned mixture of fine clay 

 and sand, containing as much of the former as 



