8 9 



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

 donia and Tharnnolia. 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 yfep/troma, 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 increases 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 Parmclia 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- 



