62 
to the naked eye. They are, however, almost exactly like 
those found on the mouldy bread, and they run both 
between and within the dead and dying cells. They can 
also be traced into and between adjoining living cells, 
and when the seedling falls prostrate the remainder of 
the plant is soon invaded, for it is kept moist by contact 
with the-damp soil. As the tissues further decay the 
filaments of the fungus spread out over the soil reaching 
across to other seedlings which then succumb in the same 
sort of way. The fungus attacks the cells of the seed- 
lings by first extracting water, then boring through the 
cell walls and finally killing the living protoplasm and 
feeding upon the cell contents. Since the fungus grows 
‘very rapidly a seedling may be reduced to a putrid mass 
in a few hours. : 
The life story of Pythium is typical of the most 
thorough and destructive of plant parasites. The fila- 
ments. at first grow in the air spaces between the cells, but 
later they enter and kill the living. protoplasm. The 
spread of the fungus at first is due to the growth over the 
soil from its earlier victims to healthy seedlings which 
are attacked in turn; but soon a more rapid means of 
spreading comes into play. When a seedling has become 
thoroughly infected by the filaments of the fungus the 
ends of many of the branches of the latter begin to swell 
out into globular bodies very like the spore-cases of Mucor, 
only much smaller. These swollen bodies are full of 
protoplasm and serve a somewhat similar purpose to those 
m Mucor. They are really special spore-cases, but in 
further development they differ considerably from those 
of Mucor. In that fungus the spore-cases were borne on 
filaments standing erect from the surface, the spores being 
shed into the air. In Pythium, however, the spore-cases 
are submerged in the film of moisture around the decay- 
ing seedling, and the different behaviour probably depends 
on this. When the spore case is mature a short tube grows 
from the side and swells to form a globular body with a 
very thin wall. Into this the whole of the protoplasm 
passes from the spore-case; it then rapidly divides into 
g or 10 small rather oval masses of protoplasm, which 
begin to writhe and wriggle within the thin vesicle. This 
soon bursts, liberating the minute writhing spores which 
swim about in the slight film of water on the soil or sur- 
face of the’seedling. When examined under high mag- 
