82 MANURES. 



and others can scarcely ever be too much 

 manured — the Pine family will hardly bear 

 any — the Cacti, which naturally vegetate on 

 rocks and in sand, will if manured attain an 

 excessive vigorous growth. The variety of 

 manures and their useful application to differ- 

 ent plants are almost infinite. 



Loamy clay absorbs heat slowly, retains 

 moisture so tenaciously as to prevent drain- 

 age, and is so compact as to hinder the passage 

 of the young spongioles of the root through it. 

 Yet mixed with a large quantity of sand, peat, 

 lime and manure, it becomes valuable ; its 

 capability of retaining moisture enabling it to 

 hold the solutions of the peat, lime, and manure 

 until gradually used by the roots, which valu- 

 able solutions would quickly run through a 

 light sandy soil without clay, before the roots 

 had time to absorb them. 



Silex or the component part of sand, when 

 dissolved by the potash, soda, or other alkaline 

 properties of manure, enters into the tissue of 

 many plants, and largely into all grassy plants ; 

 it is supposed to be the chief cause of the stiff- 

 ness or rigidity of the stem — hence it is valu- 

 able as a manure ; it also lightens heavy clayey 

 soils. Calcareous earth or lime also enters in 

 appreciable quantity into many plants in the 



