176 PLANT LIFE 
by which they have been enabled easily to 
bring about these quite definite and charac- 
teristic changes of form. It is evident that 
the physiological adjustments must be very 
delicate, for all attempts to imitate them have 
so far ended in failure. But it is just on this 
quality that the more “educated” fungal 
parasites depend for their subsistence, and 
it is a quality which they share with other 
specialised vegetable parasites, as well as with 
the gall-producing animals. 
It has already been said that all stages can 
be traced between a saprophytic and a para- 
sitic habit as exemplified in the life histories 
of different fungi. Sometimes it is possible 
to trace the change from one to the other in a 
single individual. This may occur either by 
the fungus acquiring additional powers of 
attack or it may happen through a diminution 
of the power of resisting infection on the part 
of the victim. 
As an example of the first of these we may 
select a common brown mould known as 
Botrytis cinerea. Like many of these fungi, 
Botrytis represents the mould form of one of 
the cup fungi (Peziza). 
If the spores of the peziza fructification are 
sown on a living plant, say a carrot, they 
usually fail to infect it; but if they happen to 
fall on to a dead or decaying portion of the 
carrot, they grow and produce a mycelium 
which spreads through the dead _ tissues. 
And this mycelium can now invade the living 
