410 FIRST FORMS OF VEGETATION. 
turnips, beet-root, peas, gourds, spinach, tomatoes, 
and almost all the green crops we raise, often suffer 
severely from this blight. In seasons favourable 
for their development they spread like wild-fire, 
and destroy everything before them. A closely 
allied species is the cause of the destructive plague 
affecting the grape, which shortly after the potato- 
disease broke out, spread suddenly throughout the 
vine-growing countries of Europe. The fungus 
called Otdium Tuckeri (Fig. 50), concerned in this 
epidemic, made its first appearance, or rather was 
first observed, in the hot-houses of Mr. Slater of 
Fic. 50.—O1pium TucKERI. 
(a) Natural size. (6) Magnified. 
Margate by his very intelligent gardener, Edward 
Tucker, after whom, in consequence, it received its 
specific name. It seems to have been previously 
unknown to botanists. Its origin is very obscure. 
We know not whether the germs of the fungus 
spread from those produced in the hothouses of 
Margate, or whether similar conditions elsewhere 
