64 
The South /lustraliafi Naturalist. 
■ \iaiiy interesting views liavc been advanced concerning the 
relationships between the fungus and the alga of the lichen thallus, 
At one time it was thought that parasitism might explain it, the 
[imgus being assumed to prey upon the alga, but the long healthy 
life of both organisms does not suggest parasitism, which is always 
more or less fatal to the parasitized host. Later the connection 
was thought to be one of symbiosis, where mutual growth and 
inter-dependence come into play. Some investigators held that 
the fungus derived nutriment from the algal cells as they died; 
but this hardly alloW'S for the normal wastage of all organic beings, 
and the presence of a few dead algal cells in the thallus as a whole, 
l^erhaps no more fantastic view has been advanced than that t;he 
connection is one of hlelotism (Greek Heilotes, a slave). It was 
thought that the fungus was the master and the alga the slave. 
The fungus certainly predominates in the union, but it is now 
thought that each component provides something that the othei 
cannot supply or exist without, so that there is a mutual benefit 
in this ' strange association. 
A Crustaccous Lichen showing ‘‘Chinking.'’ 
'I’he many species of lichens fall naturally into three growth 
types, namely crustaceous, foliaceous and fruticulous. ^ The crus- 
taceous forms are the simpler and grow closely applied to their 
substratum, so that they reproduce fairly accurately the contour 
of the surface upon which they grow. The upper surface 
thallus of these forms frequently show^ division Into many-sided 
]X)rtions, separated by deps chinks. These have the appearance 
of cracks, but they are more than that because they^ are part oi 
the lichen organisation. This chinking has a physiological signi- 
ficance; in Summer the many-sided areas are wddely separated, 
but on the application of water, the chinks close up, very little o 
llie water falling on them is lost, and while it lasts the henen 
