8 
president’s address. 
a hedgerow plant in Norfolk, and even at the present time it is but 
rarely encountered growing in these places. Subsequent examina- 
tions by scientific botanists, aided by the microscope, of the parasite 
itself, showed that the fungus on the Barberry was totally unlike 
that upon the Wheat plant, and these two states of it were long 
regarded as not only being different species, but as belonging to 
distinct genera. It was not until 1865 — 6 that Professor De Bary 
demonstrated their identity by means of biological research. 
Although differing so much in the size, and in the form, and in the 
colour of their spores, yet they do not differ more from one another 
than the tapeworm does from the hydatid. To the peculiar habit 
the fungus possesses of spending a part of its existence upon one 
plant and the other upon another of a totally different kind, the 
term heteroecism has been applied. But the whole chapter of the 
life history of the Wheat mildew is by no means closed by these 
observations of De Bary. 
The fungus, under its ordinary conditions, presents itself in three 
distinct forms. First, upon the Barberry, in groups of beautiful little 
cups, edged with white teeth, and filled with golden yellow spherical 
spores. These spores, if they chance to fall upon a healthy Barberry 
leaf, are incapable of reproducing the parasite upon it ; but if they 
fall upon Wheat or upon certain other cereals and grasses, they in 
due course produce the second stage of the disease — the condition 
known popularly as “rust.” These rust-spores are not developed 
in cups at all, but in little oval pustular heaps ; the spores them- 
selves are darker in colour, and instead of being spherical in form 
are oval. Placed upon a healthy Barberry leaf they are incapable 
of affecting it, but when applied to a healthy Wheat leaf they 
originate fresh pustules of rust. The function of the rust-spores 
then is to spread the disease upon the Wheat plants. After a time 
we meet with the third form of the disease, the true Wheat mildew. 
This presents itself in the form of black lines, principally on the 
leaf-sheaths and stems. These lines are so solid and compact in 
their structure that they split up the affected stems in a very 
characteristic manner. The mildew-spores are dark brown in colour, 
bicellular in form, and remain firmly attached by their bases to the 
