8 9 



various modifications of the thalloid exciple and the podetia of Cla- 

 donia and Thamnolia. The form of the thalloid apothecial cup favors 

 the function of assimilation rather than the distribution of spores, 

 yet there are a few apothecial adaptations which would seem to aid 

 in this process. In Nephroma, for instance, the apothecia occur on 

 the lower surface of the thallus ; in the early part of its development 

 the thallus-lobes lie horizontally flattened and no doubt afford a pro- 

 tection to the developing apothecium ; when the spores are maturing 

 the thallus-margin is turned upward at an angle of usually less than 

 90 , rarely more ; the mechanical force is supplied by the excipular 

 margin which increas.es in thickness more rapidly than the opposite 

 (superior) cortical layer which is passively bent ; with apothecia in 

 this position the ejected spores are least liable to adhere to the 

 apothecial disk and are readily acted upon and carried away by air 

 currents. In Parmelia -perforata we find very large cup-like 

 apothecia, and it is evident that the majority of ejected spores must 

 remain in the cup if no provision were made for their escape ; this, 

 however, is provided for by an opening at its base. 



With these perhaps doubtful exceptions there seem to be no special 

 adaptations for the distribution of lichen-spores. It must also be 

 borne in mind that the adaptations for the ejection of spores are not 

 derived during the phylogenesis as lichens, but are a direct acquisi- 

 tion and transmission from the fungal ancestor. 



|/ 2. THE GERMINATION OF SPORES. 



The germination of spores has been investigated by various au- 

 thors, especially with a view to studying the relation of the spore 

 product to the gonidia. We shall here limit our observations to the 

 development of lichen-spores in general, without discussing their re- 

 lation to the algal symbiont. 



If the spore falls upon a suitable nidus it prepares for germination, 

 either at once, or not until after a period of several weeks or months. 

 A definite amount of moisture and warmth is all that is required, 

 as the spores contain within themselves a sufficient quantity of stored 

 food substances to allow the formation of the " promycelium " or 

 " protothallus." 



The initial changes observed are as follows, and occur in all 

 germinating spores : The spore increases somewhat in size, the 

 plasmic contents become more granular, the oil-globules are emulsi- 



