Fink : Classification of Lichens 
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these plants. Forms that appear to be closely related must be 
studied together, whether all are algicolous, all non-algicolous, 
or part of them one and part the other. Nor is it necessary that 
one worker should attempt to study all Ascomycetes, except in a 
very general way. 
Another difficulty is that lichen descriptions have usually been 
based upon the assumption that the alga forms part of the lichen. 
Lichenists, even those who believe that lichens are fungi, still 
for most part continue to give, in their descriptions, details regard- 
ing the size and the form of the algae enclosed within lichen 
thalli. Statements regarding the algae should not be given as a 
part of descriptions of species, genera, or larger groups of lichens, 
but should follow or precede the descriptions. The changes 
needed are greatest in those lichens which grow throughout the 
algal colonies. The well known Collema pulposum (Bernh.) 
Ach. will serve as an illustration. The thallus has been described 
hitherto as orbicular or irregular, middle-sized, very gelatinous 
when wet, frequently showing a rosulate arrangement of the lobes, 
rather thick especially toward the center, leek-green, olivaceous or 
blackening, the lobes repand-crenate, etc. This is mainly a de- 
scription of the algal colony in which the lichen is imbedded. 
The lichen thallus should be described somewhat as follows : thal- 
lus a loose network of hyaline, septate, branching hyphae, which 
are 2.5 to 4 mic. in diameter, with cells 15 to 30 mic. long; simple 
rhizoids hyaline to light brown, with cells 4 to 5.5 mic. in diam- 
eter and 20 to 25 mic. long. Then may follow a description of 
the sexual reproductive organs and of the apothecium and its 
parts. Following this the algal colony in which the lichen grows 
may be described in a separate paragraph. The description of the 
Collemaceae as a whole and all the genera and species will need 
to be modified in similar fashion. What are specific and what are 
generic characters will appear in the revision. What species will 
have to be abandoned because of excluding from the descriptions 
the characters which belong to the algal hosts can only be ascer- 
tained by critical #tudy. 
The changes required in the descriptions of those lichens which 
contain the symbiotic algae in a stratum within their thalli will not 
be so great, and fortunately these lichens are far more numerous 
