81 



the work of r'unfstiick. I wish to refer to one point only. While 

 it is (generally atimittec! that the lichen components or symbionts 

 may develop and exist independently under artificial conditions, 

 at least up to a certain stage, there is no evidence that such is 

 the case in nature. The statement has been made that the algal 

 symbiont may escape from the thallus and vegetate independently 

 on bark, etc., but it lacks proof. Iwen though that were the 

 case, the fungal symbiont does not exist independently in nature 

 and hence a lichen is an impossibility without the mutualistic 

 association of alga and fungus. No one has yet succeeded in 

 forming a lichen by associating a true alga {Cystococcus) with a 

 true ascomycctous fungus. If this were possible we might reason- 

 ably expect spontaneously synthetic lichen formations in nature, 

 which is certainly not the case. Lichens invariably arise from 

 preexisting lichens. Some authorities state that a fungus may 

 attack nostoc colonies and transform them into collematous 

 lichens but this statement requires verification. 



Therefore, without entering into what would merely be useless 

 discussion and repetition, it would appear to the writer that the 

 most plausible and reasonable attitude to take toward lichen clas- 

 sification is to consider them as a distinct class. This is the con- 

 clusion reached after a perusal of the more important literature 

 on the subject and a rather careful study of the morphology 

 (gross and minute) and ecology of the more important represen- 

 tatives of this very interesting group of plants. 



While the system proposed by Zahlbruckner is undoubtedly 

 the best in existence, there are nevertheless several changes 

 which would appear to be desirable. Fiinfstiick calls attention 

 to the fact that our knowledge of certain lichen structures, 

 organs, functions, etc., etc., is as yet not well understood owing 

 to the fact that our knowledge of lichen evolution and licherv 

 ecology is very incomplete. This accounts for our indefinite and 

 variable terminology. With few exceptions we know practically 

 nothing of the delimitations of species. While this applies espe- 

 cially to the lower forms, it applies also to some of the higher 

 forms, as, for example, Usnca barbata, many of the Parmelias, 

 some of the Cladonias, and others. In consideration of these con- 



