On IVIieat Mildew. 
501 
and straw throughout the winter, and show no signs of life till 
the spring, when, under favourable conditions, they begin to 
germinate. Each of the two cells of which the spore is corn- 
Fig. 5. — Section through part of the Straw of Wheat, showing the Bipe 
Spores of the Mildew. 
posed sends out a short filament, that terminates in three or 
four branches. The tips of these branches swell, and another 
kind of spore is produced, after which the filament dies. These 
minute and delicate spores develop a mycelium only when they 
germinate on the leaf of the barberry. The germinating fila- 
ment does not seek admission to the leaf through a stomate, but 
it has the power, like the spores of the fungus which causes the 
potato disease, of penetrating the skin where it germinates, and 
passing directly into the tissues of the leaf. There it rapidly 
grows, and in a short time produces the two kinds of fructifica- 
tion which have been already described. 
This remarkable narrative of the year's life of this parasitic 
plant was foreshadowed, as has been pointed out, by Professor 
Henslow in a paper printed in this Journal forty years ago. 
The injury done to the wheat by the rust and mildew arises 
from the fungus appropriating to its own use the elaborated 
juices of the wheat. Fungi are plants without the green 
colouring matter, or chlorophyl, which exists in other plants, 
and they are consequently unable to separate the carbon from 
the carbonic acid gas of the air, that is, to manufacture plant- 
food from the raw materials on which plants live. They 
therefore depend on the already prepared food of the plants on 
which they are parasitic. The fungus in its rust-stage takes 
possession of the growing plant, and weakens it so far as it 
