When a moist atmosphere is duly and regularly maintained, there is but little fear need be entertained of the establishment of a colony of insects--such as the thrip, and the red spider, which are perhaps the greatest pests which have to be overcome in the forcing house; nor is there a more effectual method of destroying them, than by applying a high temperature in conjunction with an intense degree of moisture. To the want of a balance of moisture in the composition of the atmosphere, and in the soil, too, rather than as is commonly supposed, to an excess of it in the former, is the appearance called mildew to be attributed; this it occasions by checking the regular action of the perspiratory organs, and thereby inducing an eruption of the cells of the tissue: the extravasated sap lodging on the cuticle, affords a nidus for the germination of the sporules of that particular fungus, which when grown, is the mildew: the remedy consists in avoiding an irregular composition of the atmosphere, as regards heat and moisture; and also an excess or deficiency of moisture in the soil, so that each may be in a condition to exert its proper influence on the constitution and developement of the plants. Canker, another disease, to which Cucumbers are sometimes subject, appears to be produced by too low a degree of temperature, accompanied by an excess of moisture, both in the soil and the atmosphere, and it generally attacks those particular parts, where any check or obstruction is offered to the flow of the sap, such as that occasioned by a wound, or even the ramifications of the stem: this suggests that its remedy, would consist in a due regulation and balance of the constituents of the atmosphere, and the soil. Moisture is generally applied to the soil by being poured directly on it, and to the atmosphere, by means of the syringe, and the use of evaporation troughs. When applied to the soil only from the upper surface, there is a liability of its failing thoroughly to moisten it, and by reason of this, together with the constant action of the heat from below, by whatever means heat may be applied, the soil is frequently found to be dry beneath, when the appearance of the surface might lead to the supposition that it was sufficiently moistened.