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its fungal symbiont. This has been repeatedly demonstrated ex- 
perimentally. Considered as a unit, the fungal portion of the 
lichen supplies the algal with water, the necessary mineral sub- 
stances, N., O. and H., from the underlying substratum and air. 
The algal symbiont as a result of this unusual supply of food ma- 
terials, forms an extra amount of carbon and nitrogenous com- 
pounds, which is assimilated by the fungal symbiont. Thus it 
is seen that the benefit derived from this association is mutual. 
The term “mutualism,’ proposed by Tubeuf, is very appropriate 
and may well supplant the equally correct but more complex ex- 
pression “ mutualistic symbiosis,’ proposed by Frank. 
Reproduction by means of soredia stands without a parallel 
in the vegetable kingdom. They are of course asexual, and are 
formed in the algal zone of the lichen thallus by the symbiotic 
association of algae and hyphae. They may be designated as 
mutualistic brood buds. They are really vegetative reproductive 
organs, and on that account the objection may be raised that they 
are not true reproductive organs. I shall not here enter into a 
discussion on the ultimate difinition of reproductive organs. The 
fact remains that soredia alone contain the necessary elements for 
JSorming a new lichen. There is no doubt that the great majority 
of lichens are reproduced from soredia; in fact, this is the only 
means of reproduction in some species. The outer semi-cortical 
hyphal layer of soredia enclosing the algae maintains a sufficient 
‘degree of moisture to enable them to lie dormant for a long 
period of time, or until conditions are suitable for their develop- 
ment. They are certainly far more reliable than spores (associa- 
ted with the necessary algae) as reproductive organs. In fact, as 
Reinke has indicated, lichen reproduction by the aid of spores is 
in most respects similar to reproduction by means of soredia. In 
Endocarpon pusillum, for example, some of the algae are ejected 
and with the spore adhere to the mucilaginous spore wall, thus 
forming a sort of soredium in which the spore represents the 
fungal element. If the algae are not ejected with the spores, the 
chances for developing a new lichen must indeed be slight, for 
reasons already given. 
In my opinion sufficient reasons have been given why lichens 
cannot be classed with fungi, much less with algae, and must 
