DISEASES OF GREENHOUSE PLANTS. 271 



greyish-white fihn of growth spread over the surface of 

 the leaf. Plants that are much crowded, and do not get 

 sufficient light and air, are specially liable to an attack. 



Remedies. — Spraying with the sulphide solution advised 

 for Leaf Eust will destroy the mildew, and also prevent it 

 again infecting the foliage. Dustings with flowers of sul- 

 phur will also prove effectual. Extremes of temperature, 

 when the plants are housed, should also be avoided. 



Damping:-off Disease.— Every plant-grower has at 

 some time or other had the mortification of seeing valuable 

 seedlings wither and fall over on their sides in the seed- 

 pot or box. The stems shrivel just at their junction with 

 the soil. This is caused by a fungus technically known as 

 Pythium de Baryanum. It appears to infest soils that 

 are kept too moist. 



PiEMEDiES. — Directly the seedlings show signs of attack 

 pull out the infected ones and dust sulphur among the 

 remainder. Stand the pan, pot, or box in as light a posi- 

 tion as possible, and do not water too freely. 



Mildew. — There are several kinds of mildew attacking 

 greenhouse plants, but all are pretty much alike, and 

 amenable to the same course of treatment. Mildew is a 

 name commonly applied to several kinds of minute fungi 

 of a parasitic nature, and which grow upon the leaves or 

 shoots of plants. Seen under the microscope, they con- 

 sist of slender threads which spread over the surface of 

 the leaves, and here and there put forth suckers which 

 penetrate the cells and thus thrive on the sap. In due 

 course these minute parasitic plants bear millions of 

 spores, which are carried by the agency of the wind to 

 other plants, and hence the fungus spreads very rapidly 

 if not checked. Mildewy as seen by the naked eye, is a 

 dense whitish mould. It generally makes its appearance 

 in greenhouses kept too dry or too moist, and where pro- 

 per attention is not paid to ventilation. 



Remedies. — Avoiding extremes of dryness and moisture, 

 both in the atmosphere and at the roots of the plants, is 



