sheet roi 
conditi 
favourable to 
f 
Structure of an 
onion leaf. 
g 
All growth of the bulb is arrested as soon as the fungus has taken a 
good hold on the onion plant. This is due to the fact that the nutrition 
and other functions of the plant are interfered with by the presence of 
the fungus living paceniticaliy upon the onion leaves. The fungus does 
not itself attack the bulb, and the bulb does not rot, so that if the 
plants are akd when fully grown or almost so, the crop is not 
destroyed. 
On its first sppoaranoo the fungus has a stimulating effect upon = 
growth of the onion plant. This is shown the “shooting up o 
long neck between 1 the top of the bulb and the base of the leaves ; or, 
in other words, instead of the leaves separating from one another at the 
top of the bulb, long ~ is formed between the bulb and the base of 
the leaves, Fig, 1. e pressure of this stalk is a sure sign of the 
as of the disease, and it affords a ready means of recognising 
ted plants in a large patch of onions. 
r 
conditions of the atmosphere which are favourable to the 
development and growth of the fungus, and hence to the progress of the 
disease, are heavy dews or rains followed by warm paoia calm weather, 
and the absence of direct sunlight and strong winds. ady and 
sheltered spots are usually the most liable to be tiie 
The land along the south side of Bermuda usually keeps free from 
the disease, and this freedom from attack is attributed by the guam 
to the fact that there the onion plants are exposed to the early morning 
sun and aY = prevalent northerly winds, which rapidly cause the dew 
to evapor. 
e progress of the disease is sometimes arrested, after it = 
is rarely the case; as a rule, when it has once appeared > spice with 
Secr: IL—Tuer Satta AND LIFE- cree OF THE FuNGuUS 
NOSPORA SCHLEIDENIAN 
In order to fully understand the structure of the fungus Peronospora 
Schleideniana and the various stages of its growth, or its “ life-history,” 
it will be necessary ta pa some idea of the structure of the onion leaf 
upon which it flouri 
and in the cells near the surface the green substance termed 
chlorophyll, ye gives the plant its characteristic colour. These cells 
are shown at © ig. 
The cells are a on the outside by a special layer of cells, which 
form an outer skin for the leaf. These cells, shown ig. 3., 
iffer somewhat in appearance ae those within. The layer which ‘they 
ry ie is termed the 
mewhat closer Sheer vation of the slice of onion leaf, it will be 
t 
intercellular spaces are shown at 1r., Fig. 3. In other w the 
cells are not packed closely together as bricks in a wall, but PEREA 
a exist Dinie them, as between bricks when piled up roughly in a 
