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In ‘considering methods for preventing this disease it 
is necessary to make use of the facts which are known of 
the means of spreading of the fungus causing the disease. 
We have seen that once a seed-bed is infected the fungus 
rapidly spreads, first by an abundant growth of filaments 
over the soil from seedling to seedling, and secondly by 
means of spores which swim in the water in the soil. Any 
treatment to be successful must check the vegetative 
growth of fungus in the soil and also the production of 
spores. It has been shown that the fungus only grows in 
this way in warm, very moist, badly ventilated seed-beds. 
Moreover, the effect of excessive moisture and lack of 
sufficient air is two-fold. Not only do such conditions 
favour the growth of Pythiuim, but these verv conditions 
tend to produce weak drawn seedlings which of course 
are more susceptible to attack. Very careful attention to 
cultural conditions will therefore make it possible to ward 
off and, in most cases, entirely prevent the disease. The 
seedlings should never be overcrowded, and they should 
be given as much air and as little water as possible. If 
through inattention to these conditions a few of the seed- 
lings in a bed should show signs of disease they should 
be immediately removed and burned, and more air and 
less water given to those that remain. In any treatment 
it is also necessary to prevent the infection of the seed-bed 
at the beginning of the season. This infection invariably 
arises from the presence of resting spores fn the soil. 
Naturally, then, soil known to have previously produced 
the disease should not be used, but since the resting spores 
are present in most garden soils it is wisest to endeavour 
to get rid of them. They can be killed by partially 
sterilising the soil by heating with steam or with boiling 
water. It has been shown in an earlier lecture that the 
See sterilisation of soil is valuable for other reasons. 
y adopting the practice it is possible to eliminate the 
resting cells note only of Pythium but also of other 
harmful organisms. 
