180 LEAF AND SEEDLING DISEASES 
with a suitable seedling, it settles down and germinates with 
a germ tube which forces its way into the seedling at some 
point where two epidermal cells touch each other. The 
germt ube then branches and quickly forms a mycelium 
which may spread through a considerable part of the host. 
Sporangiophores and sporangia are produced in a few days 
anda new cycle is commenced. 
In this way the disease may 
b spread very quickly and 
whole seed-beds may be com- 
pletely exterminated in a 
very short time. 
Bf The fungus has a special 
means of perennation, i.e. 
living overthe winter. Certain 
hyphae inside the seedling 
become swollen at the ends 
and form female organs. 
\ B 
Fie. 73.—a, Sporangiophore of 
Phytophthora omnivora: a, stalk ; 6, 
young sporangium ; c, sporangium 
ready to fall. s, Conidiophore of 
Fusoma parasiticum: a, short 
hyphae bearing conidia ; b, young, 
unseptate conidium; c, mature, 
Other hyphae by the side of 
these become converted into 
male organs. A fusion takes 
place, and a large spore, 
called the oospore, is formed 
septate conidium. ts 
inside the female organ. 
This oospore puts on a very thick wall, and contains 
sufficient food material to live through the winter. In the 
spring it divides up into a number of swarm-spores like 
those which are set free from the sporangium. 
Attacked seedlings show dark patches, especially near 
the surface of the ground, and quickly collapse. Remedial 
measures will be considered after the other damping-off 
fungus has been described. 
Fusoma parasiticum, Tub., also attacks the seedlings of 
nearly all species of conifers. Like the last fungus, it causes 
dark patches and the collapse of the seedlings. In damp 
weather a greyish mycelium appears on the outside of 
attacked parts, and this mycelium bears slightly curved 
septate conidia (fig. 73,B). These are genuine conidia, and 
