Page:Vegetables and their Cultivation.djvu/135

Rh rapidly as to be, at the present time, the most destructive parasite with which the cultivator of cucumbers and melons has to contend. Many market growers have been obliged to give up the cultivation of the crops, whilst others report a loss of £2,000 annually. The first symptom is the appearance of pale green spots, scattered about on the surface of the leaves. These spots gradually spread until they run together, and at the same time pass through a grey to a brownish colour. This is the fruiting stage of the fungus. If it be examined at this time with a lens, it is found to consist of a lot of fine, upright, brown threads, each bearing a fruit or "conidium" at its tip. These conidia are the reproductive bodies, and can be carried from diseased to healthy plants on currents of air, clothing, or insects. Sometimes the leaves dry up and fall to the ground, when the "mycelium" present in the tissues quickly grows, forming cobweb-like threads, which run on the surface of the soil, producing more conidia. Failing food, the disease passes into a resting state, in which form it may remain inactive in the soil from season to season, only to spring into life again on the advent of warmth and moisture. These latter conditions are absolutely necessary to the pest, and so it can only attack plants under glass, attempts to inoculate plants grown outside having failed. There is said to be no risk of infection from the seeds.

—The foliage should be kept as hardy as possible, by the admittance of as much air as possible, and the atmosphere should not be kept any moister than is absolutely necessary. Spraying in anticipation, with a solution of two ounces of potassium sulphide in three gallons of water, adding two ounces of soft soap, is recommended. The under sides of the leaves should be carefully sprayed and the soil well drenched with the solution if the disease is present. Diseased leaves should be removed and burnt. After a crop has been taken out, the soil should be soaked with a solution of "Jeyes' Fluid," one ounce to the gallon of water.

Cucumber Rot (Hypochnus cucumeris).—A fungus which in the form of a grey, film-like growth, attacks the stems of cucumbers near the soil, causing them to die.