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of spermagonia may safely be conjectured. To say the least, it 
is certainly unreasonable to assume that spermatia will at one 
time function as non-sexual spores, and at another time as male 
sexual organs. Further investigations will reveal the true nature 
of things. The sooner this is accomplished the better, as many 
lichenologists have already made the deplorable mistake of consid- 
ering spermagonia as important characters in lichen classification. 
To classify plants according to the characteristics of the parasites 
found upon them would certainly be a questionable procedure in 
modern taxonomy. 
Other characteristics which distinguish lichens from fungi are 
the presence of various chemical compounds, notably lichenin, 
which is never found in fungi. 
Characteristics which distinguish lichens from fungi also distin- 
guish them from algae. There is certainly less similarity between 
an alga and a lichen than there is between a fungus and a lichen, 
though several attempts had been made to classify them as algae. 
In general it may be stated that lichens resemble algae only in so 
far as the algal symbiont resembles algae. The differences will be 
brought out in the discussion of those characters which separate 
lichens from both algae and fungi. For convenience sake I wil! 
separate these characters into morphological and physiological. 
These are the characters which fully establish the autonomy of 
lichens. 
MORPHOLOGICAL. 
Lichens, macroscopically considered, have such a peculiar ap- 
pearance that the most superficial observer is naturally led to 
suppose that they form a group by themselves. They are found 
in places where neither alga nor fungus can exist alone. Especially 
peculiar is their ability to resist low temperatures. Freezing only 
checks their growth. A temperature of —40 ° C. does not kill them. 
Such crude observations are however not sufficient to establish 
their individualism. 
The lichen thallus is of special interest to the morphologist 
since this structure is typically lichenological. It always consists 
(Of the hyphal and algal symbionts. The algal symbiont is usually 
More centrally located, being surrounded by the hyphae of the 
