Oxygen, heat and moisture are the requirements for germination, but successful results are largely dependent upon proper soil selection and preparation. Many kinds of seeds cannot germinate in stiff clay soils which are devoid of humus. Air can scarcely enter such soils. The largest seeds may germinate in extremely heavy soils, but most of the garden seeds demand a soil of the best physical condition and of fine texture. The failure to get a good stand of plants is often due to clods and coarse particles of earth, which cause the soil to dry out quickly and which prevent it from coming into direct contact with the seeds. This is a, matter of prime importance. In a well-prepared soil each particle is surrounded with a film of water, and when a large number of these are in contact with the seed ample moisture is supplied for germination. A fine seed bed, therefore, is necessary for a high percentage of germination. This applies to sowings made under glass as well as in the open. Seed beds are generally improved by the application of rotten manures, and sand may also be used to advantage in heavy soils. Well-prepared soil is loose and friable and takes water readily, while a certain degree of firmness is also essential. When fertilizers are used before sowing, they should be mixed thoroughly with the soil, to prevent a considerable quantity from coming in direct contact with the seeds and causing serious injury.