330 
Garden Work 
ONION MILDEW 
This is another serious disease, which sometimes does 
considerable damage to the Onion crop. It is first detected 
by the whitish -yellow patches on the leaves. This is 
caused by the mycelium or disease plant devouring the 
contents of the cells, thereby killing them and leaving 
nothing but the empty walls, which give the patches their 
characteristic colour. The bulbs are not attacked by this 
disease, but as the food is manufactured in the leaves, if 
these are attacked early, the bulbs cannot grow. As 
the mycelium matures, little branches are sent to the out- 
side of the tissue of the leaves through the stomata. 
These bear little branches, each with a spore at the apex. 
These spores are produced in large numbers, and, being 
very minute and light, are blown about by the wind. 
Wherever one alights on a healthy Onion leaf, it im- 
mediately germinates, producing a little hypha, which 
enters the tissue of the leaf and produces another centre 
of the disease. Thus, in a very short time, the whole 
crop may be attacked. Not only will the original crop 
be ruined, but insects, birds, &c., may carry the minute 
spores to a neighbouring crop and thus infect them. The 
spores may also be carried by the wind for a considerable 
distance, and wherever they alight on healthy Onions 
they start the disease. There is another mode of repro- 
duction. Towards the end of the season branches are 
given off which produce thick - walled spores that are 
able to lie dormant in the soil during the winter unharmed, 
and if they come into contact with Onions in spring, 
will germinate and again produce the disease, which in 
