Fink: Classification of Lichens 
113 
other mycologists, who treat lichens in general quite as inconsis- 
tently. On the other hand, those who believe that lichens are a 
distinct taxonomic group should, to be consistent, claim this plant, 
but they have not. The main difficulty disappears when we 
regard the lichen a fungus. The last difficulty fades for those 
who maintain that these fungi should not constitute a taxonomic 
group, but should be distributed in the best manner possible. 
Endomyces scytonematum Zuk., the last of Zukal’s half-lichens 
(152), is supposed to be Ephebe hegetschweileri Itz. The spores 
occur in naked clusters of asci, characteristic of the Gymnoasca- 
ceae. The lichen hyphae grow for a time in the sheaths of Scy- 
tonema filaments ; but as the asci develop, the hyphae penetrate 
into the trichomes of the alga, which are soon destroyed. Then 
follows, of course, the death of the lichen soon after the fruit is 
produced. Zukal took the position that we have not a lichen in 
this instance, since the relation is antagonistic and the fungus 
short lived. But mutualistic symbiosis is surely no sine qua non 
of the lichen and, indeed, seems not to exist at all in those plants. 
IMuch less is long life necessary. The early death of the algal 
host is good proof that the fungus derives benefit from the asso- 
ciation with the alga ; and the best and, apparently, the only bio- 
logical criterion for the lichen is that it should live in parasitic 
relation with an alga and at the same time maintain a relation 
with some organic or inorganic substratum. According to this 
standard, we have here a lichen which plainly belongs to the Gym- 
noascaceae. Of course, it should be left in this group, instead 
of artificially placing it elsewhere ; but in order to do so, it is not 
necessary to deny its being a lichen. 
Tobler (132) investigated a few of the several hundred par- 
asites on lichens. Among these Karschia destructans Tobler is 
described from the thallus of Chaenofheca chrysocephala (Turn.) 
Th. Fr. The Karschia penetrates into and through the crustose 
thallus of the Chaenotheca, into the bark on which the latter lichen 
grows. In passing through the lichen thallus, the Karschia 
hyphae attack and kill the Chaenotheca hyphae and the alga 
which grows in symbiotic relation with them. This gives the 
Karschia a parasitic relationship with the Chaenotheca, and with 
the alga, and a saprophytic relation with the bark and perhaps 
