VEGETATIVE MYCELIUM 
5 
same observer has noted it in Poly poms sulphureus. It is said 
to be not infrequently seen in Corticium ccBmleum. The 
phenomenon has not been satisfactorily explained. 
Another condition of vegetative mycelium is the peculiar 
nodules of variable size, at one time classed as a separate 
genus, Sclerotium. A dried sclerotium is hard and compact, 
consisting entirely of interwoven hyphae covered with a rind 
of thick brown or blackish cells. Sclerotia contain reserves 
of food materials utilized sooner or later by the fungi 
destined to spring from them. Some sclerotia and the fungi 
associated with them may be seen on Plates IV. and V. 
The abundant production of rhizomorphs and sclerotia may 
be compared with the luxuriant growth, without flowers 
or fruit, of normally flowering plants which sometimes 
takes place under very favourable conditions. 
The spores of larger fungi have no thick outer coat, hence 
have no protection against extremes of heat and cold. It 
may be inferred (i) that they germinate immediately upon 
finding a suitable matrix; (2) that the resulting mycelium 
has a resting stage; (3) that the duration of the vegetative 
stage is influenced by climatic conditions. It is almost 
certain that the mycelium does not produce sporophores if 
unfavourable conditions prevail at the time of the year 
when it is normally vigorous. With many species the 
activity of the mycelium is confined to a certain period. If 
the fungus is not produced during that time, the mycelium 
will continue to vegetate, and, given suitable climatic con¬ 
ditions, will carry out its destiny the following year. This 
is the explanation of the abundance of “ mushrooms ” in 
some seasons, and their infrequency or rarity in others. 
Apart from this compulsory prolonged hibernation, there is 
a certain amount of evidence tending to show that the 
mycelium of some species fructifies only once in three years. 
Records of appearances of fungi in certain spots around 
Haslemere have been kept at the Haslemere Museum for 
