DISEASES OF VEGETABLES. 283 



cucumber, &c., it shows itself in spots, and in dry 

 seasons it is almost always seen on the leaves of early 

 turnips, and late sown peas in the autumn. It has 

 been ascertained by naturalists that mildew is a species 

 of fungus which attaches itself to certain plants when 

 they are in a peculiar state of growth favourable to 

 its nature. If this be so, it cannot with propriety be 

 called a disease, though its effects are equally destruc- 

 tive. Luckily it is a vegetable parasite of a more 

 delicate constitution than are the plants it fixes on, 

 because it very soon yields to an application or two 

 of a strong soap lather or a lixivium of flour of brim- 

 stone and water. By these means it is easily banished 

 from trees in houses, or on walls. And there is no 

 doubt but that water slightly impregnated with soda, 

 or any alkaline salt, used as a wash, would defend 

 plants from its attack, as well as recover those already 

 suffering from it. Its appearance on turnips, and 

 particularly on peas, is said to be a consequence of 

 drought ; and that if the latter crop be well watered 

 when necessary, the mildew is prevented. 



Uredo or rust. This is a malady, or rather an 

 injury, to which cereal plants, wheat in particular, are 

 often liable. This, like the mildew, is also a fungus, 

 which seizes on the leaves and straw in such numbers 

 as to interrupt the course, or withdraw the whole 

 current of the sap. Hence the grain is imperfectly 

 filled, the colour and tenacity of the straw is destroyed, 

 and the crop, of course, generally deteriorated. 



Rust first appears on the leaves of strong growing 



