16 OUR FARM CROPS. 



soil, of course, claims our first consideration. "Wheat, we 

 know, has a very wide range of soils. In this country we 

 see it grown on wellnigh every variety, from the light silice- 

 ous soils met with in the eastern counties, and in the Green 

 Sandstone and New Red Sandstone formations, to the diffi- 

 cult and disheartening soils of the London, the Wealden, the 

 Oxford, and the Lias clays. Some soils, however, are 

 clearly more suitable for it than others. Those best adapted 

 for it are of course such as contain the ingredients neces- 

 sary for its growth and perfection in the best proportions, 

 and in a condition most available for the plant. We know 

 that wheat will not flourish in any soil unless there is a 

 certain amount of silica and potash for its stem, of silica 

 and lime for the chaff or outer covering of the seed, and 

 of potash, phosphoric acid, magnesia, and ammonia for 

 the seed. These substances are generally found to exist 

 in clays to a greater extent than in other descriptions of 

 earth; consequently, we are accustomed to look upon our 

 ^different soils as strong, medium, and light wjieat soils, 

 according to the proportions of clay they severally contain 

 in their composition. Pure clay, which is a chemical com- 

 pound of silica and alumina, would be unsuited to any 

 description of vegetable growth ; but clays are always more 

 or less mixed up with other substances which give them 

 their fertilizing value, while their own substance acts 

 mechanically in a very beneficial manner, by giving 

 tenacity staple to the soil, and by increasing its powers 

 of absorption and retention of moisture, and also of con- 

 densing and retaining the ammonia so necessary for plant 

 life. In soils containing large proportions of sand, or of 

 organic matter, but deficient in clay, we often see the 

 young plant very luxuriant at first, but without the power 

 to build up its stem, and consequently unable to assimilate 

 those substances necessary to perfect its growth and to 

 produce its seed. 



