320 
Garden Work 
sent out at one point, the mycelium or disease plant is still 
growing inside the tissue of the leaves, and even into the 
stem, and ultimately down into the tubers themselves. 
The little hyphae make their way from cell to cell by 
absorbing cell walls in their course, and devouring the 
cell contents, until they reach the tubers, where they carry 
on their work of destruction, leaving the brown patches 
on the tubers. Some of the little zoospores may be washed 
from the leaves to the soil or to any exposed young tubers. 
On these they germinate, and so infect the tubers in a 
direct manner. When the colder weather comes, this 
mycelium is arrested in its growth, but it is able to exist 
in this state during the winter. If these infected tubers 
are planted the following season, as soon as the warm 
weather sets in the mycelium begins to grow, and, making 
its way up the stem into the leaves, produces fruiting 
branches and spores, which are again able to spread the 
disease. 
Now, the above ought to have taught several lessons 
with regard to this disease. First, no infected potatoes 
should be planted; that is, potatoes with brownish spots 
on them. If any appear doubtful, it is far better to leave 
these out also. Second, care must be taken not to allow 
the disease to get a start, if possible, because when once 
the disease gets established inside the tissue of the plant 
it is impossible to get at it to destroy it. We may kill all 
the parts on the outside of the plant by spraying, but if the 
mycelium has got inside it will go on growing, and burst 
out in other places later on. Third, on no account must 
any diseased tubers be left on, or in, the ground, as the 
disease will lie dormant during the winter, but will spring 
