9 1 



the spore can produce only the fungal symbiont, but the fungal sym- 

 biont alone does not form a lichen, nor can it develop to maturity 

 {with perhaps some exceptions). This seems to indicate conclu- 

 sively that lichen-spores can not be considered as true reproductive 

 organs. 



The question now resolves itself into what part, if any, do lichen- 

 spores play in reproduction? The explanation of the function of 

 the thecial algae will suggest the answer to this question, that is, 

 the spores at most only aid in the process of reproduction. The 

 hyphae resulting from the process of germination must be biologic- 

 ally associated with the symbiotic algae before a lichen can be 

 formed. The spores can indeed germinate without being associated 

 with the algae, as has been proven time and again in culture experi- 

 ments, but they can not develop a mature spore-producing structure 

 without being united with the essential algae. There may be excep- 

 tions to this rule in the lower Caliciaceae, for example in Mycoca- 

 liciuni) which is a very questionable lichen genus, since it frequently 

 happens that no trace of a thallus can be found ; its species are per- 

 haps true fungi. The same may be said of some species of Pyren- 

 ula and Pyrenastrum. 



On further consideration it becomes evident that the spores are 

 very unreliable even as aids in reproduction. Since the spores are 

 distributed by air currents, it is also evident that their falling upon 

 a locality in which the required symbiotic algae occur must be 

 purely accidental. Even if this accident does happen, there is only 

 a slight chance for the formation of a new lichen, for several reasons ; 

 the spore may not be ready for germination ; in the meantime un- 

 suitable climatic conditions may destroy the algae ; and if the spore 

 subsequently develops, there may be no algae with which to enter 

 into a symbiotic relationship and as a result the "promycelium" dies. 



Another problem of great scientific importance is to find the true 

 relation of different lichen-spores to one and the same algal symbiont. 

 As already explained an algal form closely related to Cysiococcus 

 humicola occurs in the majority of Ascolichenes. The important 

 question for consideration is to find whether the various spores of 

 lichens in which this alga occurs can develop into new lichens if 

 brought in association with the alga of Parmclia perlata or any 

 other alga selected from the group of the lichens mentioned. Some 

 experiments which have been made in regard to the synthesis of 



