132 
Mycologia 
algae take much carbon from the substratum, except in cultures, 
may well be doubted. It is scarcely likely that they live a purely 
saprophytic life in nature as they may be made to do in artificial 
cultures. It is, on the other hand, much more reasonable to sup- 
pose that algae confined in lichen thalli accomplish part of their 
carbon assimilation saprophytically in the absence of abundant 
light and air. Lindau (8i) noted that Trcntcpohlia seems to 
flourish better in darkness of deep layers of bark than in the 
better lighted portions ; and it is reasonable to suppose that those 
algae which live in the bark of trees are nourished somewhat 
like fungi, whether serving as algal hosts for lichens or not. 
As stated above, Artari (5) found that the algal hosts of 
Xanthoria parietina (L.) Th. Fr. and Placodinm mnroriim 
( Hoffm. ) Ach. grew on peptone and sugar containing media in 
absolute darkness and in light with CO2 excluded, and remained 
dark green for the time that the cultures were run, — about one 
half to two and one half months. These algae grow well on min- 
eral salts under the same conditions, but not so luxuriantly, and 
are usually pale green on these salts. In such cultures, the 
peptone doubtless serves for nitrogen and the sugars for carbon. 
Artari tried several modifications of media with varying results. 
This confirms again the view that the algal hosts of lichens are 
not very dependent upon light or air. Yet it is doubtless true that 
the algae in lichen thalli work at a disadvantage on account of 
scarcity of light and air, and could perform carbon assimilation 
better with both of these present in larger quantity, such forms as 
Trentepohlia being excepted perhaps. Artari (6) carried on 
similar experiments with Stichococcus bacillaris, the algal host 
for certain lichens, with results like those stated above. 
Regarding the general relation of lower algae to carbon assimi- 
lation, Artari’s final conclusion (7) is more extreme than might 
be expected. He thinks that these plants are more dependent 
upon the nature of the substratum for chlorophyll production than 
upon either light or CO,. He found that certain lower algae 
remain colorless on certain media with light and CO, admitted, 
but are deep green on other media with light and CO._, absent. 
This rather independent relation of such plants to light and CO, 
