54 



Both forms of cyphellae are sufficiently large to be seen by the 

 naked eye. They are distributed over the convex areas of the lower 

 surface of the thallus ; none ever occur in the grooves. As already 

 explained, they begin their development near the tip of the growing 

 thallus, reaching their mature size at a distance of a few millimeters 

 from the margin. In thalli whose lower surface is nearly flat, they 

 are quite uniformly distributed. 



Acharius applied the term cyphellae to the form first described ; 

 the second form he believed to be soredia. Nylander retained the 

 name cyphellae for the first form ; the second he designated as 

 pseudocyphellae. There is no morphological or physiological 

 reason why the, latter should be designated as "false." Indeed, it 

 would be more consistent to designate the former as false, since they 

 are of less frequent occurrence. Stitzenberger (1895) retains 

 Nylander's distinction as to true and false cyphellae and further sub- 

 divides them as to color into white and yellow. This author also 

 considers these structures of great importance in his classification of 

 the Stictei. 



Having thus briefly treated the morphology of the cyphellae we 

 will refer to their probable physiological significance. As already 

 indicated, some of the older lichenologists looked upon them as vege- 

 tative organs of propagation, similar to the soredia. They are not 

 soredia, since they usually contain no algae. That the second form 

 may accidentally contain a few algae in its meshes, is possible, as we 

 find occasional groups of algae distributed throughout the entire 

 medullary layer. It is, however, unreasonable to suppose that they 

 normally contain algae, since their position is not suitable for the ready 

 development of these symbionts. There are several reasons which 

 make it seem probable that the cyphellae have to do with the func- 

 tion of aeration. As already indicated, the breathing pores are 

 analogous in function to the stomata of higher plants ; from the 

 relation of the cyphella to the breathing pores it is quite reasonable to 

 assume that their function is to admit air into the interior of the 

 thallus ; in their mode of development and in position they are 

 analogous to lenticels. It is also found that the upper cortical layer 

 of Sticta and Stictina is usually without breathing pores, which is 

 accounted for by the fact that the lower cortical layer contains the 

 necessary pores and openings for the admission of air. 



