498 
On Wheat Mildew. 
leaf, which, when carefully examined, is found to be a little cup 
full of free, round, and very minute bodies. A still more minute 
examination of the leaf will show that the fungus has another 
form of fructification on the upper surface of the leaf, where one 
may detect some scarcely perceptible pustules, through the central 
Fig. 2. — Section of a Portion of a Barberry Leaf attached hy the 
JEcidiuin, showing the two Jcinds of Fructification. 
pore of which protrude a small bunch of minute hairs. In 
section and under the microscope these pustules are seen to be 
the openings of small flask-shaped bodies filled with the delicate 
needle-like hairs which protrude themselves through the opening. 
Towards the base of the flask may be detected numerous very 
minute round bodies, the function of which has not yet been 
clearly ascertained. The larger cups opening on the lower surface 
of the leaf are found to be equally well defined, and to be enclosed 
in a distinct covering. At first appearing as little spores, they 
increase in size until they burst through the skin, and the apex 
breaks in a more or less regular manner, forming a margin to 
the cup, which is filled with minute round bodies of a reddish 
colour. These are the spores from which the next stage of the 
plant is developed. 
Both forms of fructification grow on very delicate fungal 
threads, called mycelium, which penetrate the leaf in every 
direction, and withdraw from it the food required for the life 
and growth of the parasite. 
The quantity of spores produced in the cups on a single bar- 
berry leaf is enormous. It is impossible to realise the myriads 
of fungal spores which are floating in the atmosphere during 
the greater part of the year, ready, whenever the fitting physical 
conditions are present, to germinate. No place is free from 
their presence. They are so minute that we see them only as 
