500 
On Wheat Mildeic. 
a week or ten days one can detect the presence of the fungus in 
the wheat by linear reddish swellings on the leaf and stem. 
When ripe, the skin bursts, and innumerable oval red spores 
are exposed and dispersed. 
When the suitable conditions are present, these spores germi- 
nate on wheat or on other grasses, the growing tubes pass 
through the stomates, produce mycelium in the cellular tissues 
of the leaf, and in a week, more or less, a new crop of spores 
bursts the skin of the plant, and is scattered in the air. Several 
generations of this form of the fungus may be produced in the 
course of a few weeks. In the older patches, and from the same 
mycelium, another kind of fruit is produced, at first among the 
red spores of the rust, and then entirely by itself, when the 
production of the rust-spores ceases. These are the spores of 
Fig. 4. — A Germinating Spore of Bust fourteen hours after it icas shed. 
the mildew. In the drawing of the rust-spores (Fig. 3, p. 449) 
one of these spores may be observed. These new spores are 
oblong, and taper towards each end. They are composed of 
two cells, the division being across the middle of the spore. 
As in the rust, the delicate threads or mycelium of the mildew 
penetrate the cellular tissue of the leaf or stem in every direc- 
tion. The spores are produced under the skin. They form 
long narrow swellings of a brownish colour. When the swell- 
ings burst the skin, a mass of dark spores fills the opening. If 
the disease is very bad, the plant is so completely covered with 
the dark spores that it has the appearance of having been 
scorched. 
The active life of the fungus closes with the production of 
the mildew-spores. These spores do not germinate and propa- 
gate the mildew in other wheat-plants. This is done only by 
the spores of the rust. The mildew spores remain on the leaves 
