Fink: Classification of Cichens 
131 
furacea (L.) Mann and Cladonia sp. with similar results. Finally, 
they found the same algae growing free with lichens in their 
natural habitats and secured zoospores in similar manner from 
these. 
Itzigsohn (69) made cultures for the purpose of ascertaining 
the systematic position of Peltigera. He found that the algae 
could be cultivated independently, and that they are blue-green, 
20 or more cells often cohering in the cultures in chain-like form, 
resembling Anabena, while in other instances the cells are arranged 
in colonies resembling Chroococcus. Woronine (144) isolated 
the algae from Physcia piilverulenta (Schreb.) Nyl. and obtained 
30 to 40 zoospores from each individual in the cultures. 
It will be noted that the last section also gives something con- 
cerning cultivation of the algae separately, the two kinds of cul- 
tures often going on in such a manner that the results are best 
given together. Those who hold to the mutualism hypothesis 
have claimed that the algal hosts of lichens are more difficult to 
cultivate than the same species of algae when free, but there is 
nothing to indicate that this is true. 
The Growth of Lichen Hosts and Other Algae on Media 
WITH Light or Carbon Dioxide Excluded 
• 
Reference was made to this matter in the last section above, in 
an incidental manner. Treboux (133) found organic acids to be 
the source of carbon for a number of algae in cultures in total 
darkness. Some of the 40 algae used are Stigeodonium teniie, 
Scenedesmtis obtusus, Raphidium polymorphum, Stichococcxis 
badllaris, Plexirococcus vtdgaris, Chlorella viridis, Chlorococcum 
humicgla, Haematococcus pluvialis, Englena viridis and the algal 
hosts of Peltigera sp. and Xanthoria parietina (L.) Th. Fr. Of 
the 40 algae, about half were found to assimilate from media con- 
taining organic acids, some growine: better with one acid, others 
with another. He concluded that there is no such sharp distinc- 
tion between fungi and algae with respect to carbon assimilation 
as had been supposed, the former probably being able to extract 
carbon from a larger number of organic compounds than the 
latter. Then the method of assimilation for the lichen and its 
algal host may not be so different after all. Whether terrestrial 
