FUNGUSES 61 
the same plant, and very often there is evidence which 
goes to show that the double machinery has once been 
more effective, and that the plant has fallen back upon 
the simpler and less advanced method. Sometimes the 
double machinery seems to have forgotten how to work, 
and there are only ineffective traces of it; this is what 
is meant by the “degradation” of plants. It would 
appear that many generations back they had learned 
to use the double machinery, but now they have forgotten 
it, and fallen back in the scale. 
Generally speaking, the single set of cells is throughout 
the fungi the most important method. The Common 
Mould, for instance, occasionally forms fruit by “conjuga- 
tion” of two separate hyphz, but usually simply throws 
up a long tube with a comparatively large knob at the 
end, in which spores are formed direct. In an allied group 
of aquatic Fungi, called Saprolegniacee, the double 
machinery is present, but so far as observers have been 
able to make out it refuses to work. This group contains 
one member which attracts a good deal of attention, for 
it causes the well-known salmon disease, of which so 
many complaints are heard. It grows upon the salmon’s 
scales, and in time may cause the death of its host, 
and, which is worse, may spread abroad to the other fish 
in the river by the spores which it produces freely 
enough by its single set of machinery. 
The Potato disease I have already mentioned, but its 
effects in Ireland were so tremendous that it requires a 
fuller description. The hyphz, or tubes, run all about 
the leaf of the plant, turning it black, and causing its 
death. Meanwhile, certain tubes run up through the 
pores of the leaf and bear their fruit outside, the wind 
distributing it all about the field. Each leaf and plant 
