1887.] Mr Shipley, On the Fungus causing the onion disease. 127 
November 14, 1887. 
(1) On the Fungus causing the onion disease Peronospora 
Schleideniana. By A. KE. Surpuey, B.A. 
The onion disease of the Bermudas is caused by a fungus 
Peronospora Schleideniana, which lives parasitically upon the 
leaf of the onion plant. 
The atmospheric conditions which favour the progress of the 
disease are heavy dews or rains followed by warm, moist, calm 
weather, and the absence of direct sunshine and cold winds. In 
favourable weather the progress of the disease is very rapid. 
The fungus lives in the tissues of the leaf, choking up the 
air passages and absorbing the nutritive fluid formed in the cells. 
Its stem protrudes through the stomata of the leaf into the air. 
Its branches bear spores at their tips. 
The reproduction of the fungus is effected by means of these 
spores which float about through the air, and also by means of 
certain special cells formed by the fungus and known as resting- 
spores. These pass the winter in the earth, and are capable of 
retaining the power of germination for two or three years. It is 
by their means that the disease is carried on from one season to 
another. 
One method of combating the disease is to make the onion 
plants as strong as possible, so as to withstand the attacks of the 
parasite. Hence the site should be carefully selected, the soil 
well prepared, good manures used, and the land kept clean and 
free from weeds. 
To prevent the spreading of the disease all affected plants 
must be collected and burnt. Whilst doing this care must be 
taken that the collector does not himself spread the disease by 
carrying the refuse loosely. Rotation of crops, or, when this 
is impossible, deep trenching, would lessen the chance of the 
disease appearing. 
Diseased plants may be treated with a mixture of powdered 
sulphur and freshly burnt quicklime sprinkled by hand or by 
bellows; or they may be washed or sprayed with a weak solution 
of iron sulphate (green vitriol). In both cases the fungus is 
destroyed without injury to the onion plant. Further, both these 
chemical remedies have the additional advantage of being excel- 
lent manures. 
Another fungus Macrosporium parasiticum sometimes attacks 
the onions after the Peronospora has taken a good hold of the 
plant and weakened it. As this only occurs as a sequel to the 
