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 



