1Z SOME DISEASES OF CEREALS. 
deformity of the ears is visible, sporangia are not likely to 
be found. | 
Oogonia are formed in immense quantity, at a late stage inthe 
life history of the parasite.* After fertilization they are large brown 
bodies, visible from their size and colour to the naked eye. They 
oceupy the parenchyma of the leaf blades, both of the foliage leaves 
and of those formed in the inflorescence. Very rarely they occur 
in the sheaths of the foliage leaves and in the glumes, while in con- 
trast to the foliage leaves, the sheaths of inflorescence leaves often 
contain them. ‘They are often arranged in longitudinal rows on 
each side of the veins, as a result of oogonium formation taking 
place chiefly inthe layers of parenchyma bounding the bundles, 
where, as already mentioned, the mycelium shows a tendency 
to collect. The ripe oogonium after fertilization, thickens rts wall, 
which is closely applied to the wall of the oospore without, 
however, fusing. Hence, the whole fruit is characterised by the 
possession of a very thick wall in two layers, the outer of which 
is the oogonial wall, and the inner only belongs to the oospore. 
The oospore is usually perfectly spherical, with a smooth wall, 
yellow in colour (Saccardo’s ‘‘Chromotaxia’’ No. 23), and of even 
thickness all the way round. The oogonial wall, on the other hand, 
is deeper in colour, approaching tawny (between Nos. 31 and 32 
of Saccardo), and is often irregular, being provided with thicken- 
ings, which gave the whole fruit an elliptical, angular or irregular 
shape, according to their position, but prevent it being ever quite 
spherical. The ripe fruit (plate V, fig. 9) measures 34 to 524 in 
diameter (average of 25 measurements, 42), the oospore proper 
being 22°5 to 35 in diameter (average of 50 measurements 32+). 
After trials extending over two years, I have not succeeded in ger- 
minaiing the spores, though from the evanescent nature of the 
asexual stage,and the regular manner in which the disease appears 1n 
certain places every year, it is highly probable that this occurs 
A rough calculation, made by counting the number of oospores in a measured part of 
the field of the microscope, gave 480 oospores to the square millimeter, ina portion of leaf 
where they were arranged in an almost solid mass, 
