FUNGI AND FUNGOUS DISEASES OF PLANTS 241 
fifteen or twenty minutes, and then lose its cilia and begin to 
grow into a new hypha of the mildew. These new hyphe 
may grow through the stomata of leaves and start a new 
growth of the parasite. 
Within the host leaf sexual reproduction of the parasite 
occurs, and odspores (fig. 186, C’) are formed. These odspores 
are thought to reproduce the parasite in the following spring, 
when the decay of the host leaf releases them. Our knowledge 
of odspore formation in grape mildew and potato blight is still 
incomplete. It is thought, however, by some special students 
of fungi, that potato blight has largely lost its power of sexual 
reproduction, and that odspores are not often formed.t 
229. Prevention of grape mildew and potato blight. Potato 
blight is a common and extremely destructive potato disease 
caused by a fungus that resembles grape mildew in its structure 
and habits of growth. It is readily and widely distributed and 
often causes serious losses by partially or almost completely 
preventing the growth of a potato crop. Both potato blight 
and grape mildew are prevented from reaching their normal 
growth, and are sometimes completely destroyed, by spraying 
with Bordeaux mixture.? It was in connection with a study of 
grape mildew that the Frenchman Millardet, in 1881, began 
experimenting with Bordeaux mixtures. He demonstrated the 
fact that this mixture, when properly used as a spray, will pre- 
vent most of the ill effects of grape mildew. The effect of 
using this spray in treating potatoes is well shown in figure 187. 
Many other destructive parasitic diseases of plants, though by 
no means all of them, may be prevented in the same way.? 
1G. P. Clinton, * Odspores of Potato Blight,’ Science, 744-747, 1911. 
2 The preparation as most commonly used consists of materials mixed in 
the following proportions: copper sulphate, 5 pounds ; stone lime, 5 pounds ; 
water, 50 gallons. Other proportions are often used, as indicated in agri- 
cultural experiment station reports. 
8 Dugegar, B. M., Fungous Diseases of Plants. Ginn and Company, 
Boston, 1909. 
** Potato Spraying Experiments in 1906,’’ Bulletin 279, N.Y. Agr. Exp. Sta. 
‘Certain Potato Diseases and their Remedies,” Bulletin 72, Vt. Agr. 
Exp. Sta. 
