112 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



derive their nutriment from the atmosphere alone, and are not dependent 

 on the soil or its constituents. 



Mention should be made here of certain constituents which may prove 

 hurtful to vegetation. Saline matters, if present in excess, will render 

 soil sterile. This is seen in the case of the salt plains of India and of 

 land in process of reclamation from the sea ; similarly, plants to which 

 salt has been too freely added, or which have been watered, as in the 

 instance recently quoted, with water containing much salt in solution, 

 may be injured. Ferrous salts and sulphides, again, are harmful con- 

 stituents of soils, and their occurrence is the result largely of imperfect 

 cultivation and want of aeration of the soil. By the entrance of oxygen 

 these constituents will become oxidised and rendered harmless ; lime also 

 is a potent agent in improving such soil. 



The Soil. * 



The soil may be regarded, in the first place, as the material which 

 holds up the plant, and, in the second place, as that which supplies it with 

 food. Soils differ greatly in character, according to the nature of the rock 

 or source from which they are derived, or the transport which the particles 

 have undergone. To the agriculturist these distinctions are very material 

 ones, for according to them he must shape the course of farming he is to 

 pursue. He has to take his soil as he finds it, and grow his crops as he 

 thinks most suitable ; his crops, too, must be regulated 1 y the class and 

 quality of the soil. It is impossible for him to modify, on any practical 

 scale and at any reasonable expense, the texture of his soil. To the horti- 

 culturist these differences of soil do not present such difficulties, for he 

 is able to a great extent to modify the character of the soil, and to obtain 

 for each kind of plant the soil that is best adapted for it. It is an easy 

 matter to procure for cuttings or for bulbs the sand that they do so well 

 in, or to make use of leaf-mould or peat, and it is only on the larger scale, 

 as in a vegetable garden, where the difficulty enters, for there the gardener 

 is expected to produce each kind in its turn whether the soil be suitable 

 or not. 



It would be foreign to my purpose to go at any length into the 

 characteristic features of soils of different kinds, or to set out their 

 general chemical composition ; this is a matter rather for the agricul- 

 turist than for the horticulturist. The principal classes are sandy soils, 

 loams, clays, chalky soils, and peaty soils. Sandy soils are generally poor 

 in the essential mineral constituents, potash and phosphoric acid, as also 

 in lime ; loams, which may be regarded as mixtures of sand and clay, 

 are, all round, the most useful soils for the gardener ; clays have the 

 greatest reserve of plant food, but require to be well cultivated in order 

 to make this available — they are usually very rich in potash ; chalky 

 soils, if not too rich in lime, may make good soils if well broken up, 

 and are much improved by the addition of humus — if over-abundant 

 in lime they are very apt to " burn " ; peaty soils are very rich in 

 vegetable matter, very retentive of moisture, but generally poor in lime 

 and mineral matters. 



The relation of soils to water and to heat has already been briefly 



