68 
rest after it. While it is unknown how long they can 
move about and live in the soil, they can certainly do so 
for many days. : 
In the field and garden the spores of this fungus are 
liberated into the soil by the decay of the diseased tissues 
of the infected roots. If diseased roots are left in the 
ground for any length of time the decay takes place 
rapidly and is generally accompanied by an offensive 
odour. The spores pass into the soil and there remain 
until conditions are favourable for their germination. If 
liberated during the summer or early autumn they pro- 
bably germinate at once, but if later it is likelv that they 
remain in the spore condition over the winter and 
germinate in the warmer spring days. The smallest 
quantity of water is sufficient to allow the minute specks 
of protoplasm which are liberated, to swim about. If 
young cabbages, turnips, etc. are grown in the infected 
ground the organism soon gains entrance to the younger 
roots and sets. up the disturbances described above. When- 
ever sceds of these cruciferous plants are sown in soil 
known to contain the spores of this fungus the swellings 
typical of the disease appear on the young roots in a few 
weeks. 
We have seen that this organism differs from a fungus 
like Py¢hium in several important respects. At no stage 
in its life history does it possess filaments as do the vast 
majority of fungi. It passes through the vegetative stage 
of its life as a naked speck of protoplasm living and grow- 
ing inside the protoplasm of the cells of a root. Unlike 
Pythium it does not kill the cells of its host plant out- 
right, but rather stimulates them to enlarge. divide and 
draw food supplies to them which it then utilises. | Like 
Pythium, however, it rests in the form of spores in the 
decaying roots and in the soil; it also passes part of its 
life as a naked free-swimming speck of protoplasm, but 
in order to complete its life cycle it must enter the living 
cells of the root of a cruciferous plant. 
In considering methods of preventing the attack of this 
organism it is necessary, as in all such cases of plant 
‘disease, to bear in mind the habits and life historv of the 
parasite. As has already been shown, a single diseased 
turmp or cabbage, if left to rot will liberate many 
millions of spores into the soil. Some of these doubtless 
dic, but many remain as a source of infection for future 
