9° 



fied and no doubt serve a purpose in the metabolic processes of 

 germination ; soon after a projection may be noticed at one end of 

 the body, and in some simple spores several or many of these pro- 

 jections may be formed nearly at the same time ; the exosporium 

 ruptures and the hyphal development begins. In the many-celled 

 and multilocular spores each cell may develop a hyphal branch. 



The initial hypha grows quite rapidly under favorable conditions 

 and soon sends out lateral branches ; about this time transverse 

 septa are also being formed. This first hyphal network, known as 

 the " promycelium " or " protothallus," consists of filaments more 

 irregular in size and form than the later growth and the cell-walls are 

 also thinner. If the promycelium comes in contact with the re- 

 quired algae the formation of the thallus begins as already described ; 

 if not, it perishes for want of the necessary nutrition. 



The germination of spores can readily be observed upon glass 

 slides kept in moist chambers. The greatest difficulty encountered 

 is the development of bacteria and hyphal fungi which soon stop the 

 lichen development. It should also be remembered that the growth 

 of lichens may be materially checked or entirely inhibited by ex- 

 cessive moisture. As already indicated some spores germinate much 

 more readily than others ; those of Dermatocarpon pusillum usually 

 begin development in a day or two ; those of Parmelia rudecta re- 

 quire a much longer time. It is also necessary to select fresh mate- 

 rial ; spores of herbarium material several years old will generally 

 fail to germinate. 



\ 



3- SPORES AS ORGANS OF REPRODUCTION. 



As to the phyletic origin and structure of lichen-spores there is 

 uniformity of opinion ; they are derived from and are structurally 

 almost identical with the spores of certain ascomycetous fungi. But 

 as to the true significance of these spores as organs of reproduction, 

 there is considerable uncertainty and difference of opinion manifest. 

 The true function of lichen-spores may readily be understood if one 

 has a correct understanding of the lichen as a whole, or as a unit. 

 As will be explained in the chapter treating of the polyphyletic origin 

 of lichens, the lichen-spores are structurally very similar to fungal 

 spores ; physiologically they are, however, wholly different. The 

 spore of the fungus can in all cases develop into a new individual, 

 while the spore of the lichen can not. The reason is evident, for 



