13 



central portion is sometimes empty (fistulous.) In other lichens, as 

 in CoUema, this tissue is very lax, consisting of few filaments, among 

 which the gonidia are scattered. The under side is usually of a 

 different color from the upper, and either pale or black. It is some- 

 times veiny, and sometimes covered with little cup-like white or 

 yellow depressions, Cyphellse. The spermogones occur on the upper 

 surface, or along the edges of the Thallus, as minute black (some- 

 times colored) globules, and frequently in considerable numbers. 

 The Pycnides resemble them in appearance, and are similarly situ- 

 ated. The Gonidia frequently burst into mealy excrescences, Sore- 

 dia, and the surface is often powdery, or with erect, coralloid ex- 

 crescences (Isidia.) Many merely sterile crusts were formerly 

 designated Lepraria, Variolaria or Spiloma ; but these are merely 

 sterile or degenerate conditions, not deserving a separate rank. The 

 medullary layer frequently contains crystals of oxalate of lime ; and 

 in almost all lichens there is a starchy gelatinous substance, Lich- 

 enine, formed by the dissolution of the Hyphse and the Gonidia, 

 which in the apothecia, but not solely there, is usually colored blue, 

 violet or red, by iodine, and which there is called the Hymeaial gel- 

 atine. Certain Gonidia which occur in the nucleus of Pyreno- 

 carpous Lichens are called Hymenial Gonidia ; and certain filaments, 

 resembling Paraphyses, surrounding the inner part of the ostiole of 

 such fruits are called ostiolary filaments or anaphyses. 



The Gonidia. 



The Gonidia vary in size, form, and color. The most common 

 kind arc those of a yellowish-green color surrounded by a thick 

 membrane. Such are those of Eamalina, Parmelia, Lecanora, and 

 most of the genera. Another kind are of a bluish-green color, not 

 possessing a thick membrane, which are called gonimia. These are 

 either solitary, or grouped, or concatenate, strung like a chaplet. 

 They occur most frequently in the Collemacei, but also in other 

 genera. A third kind are of a bright green or often reddish color, 

 connected together in a chain, and occur most frequently in the 

 Graphidei. In a few Lichens the gonidia are represented by a cen- 

 tral conferva-like filament with green contents. These various kinds 

 of gonidia have been referred by the supporters of the Schwendener 

 theory to different genera of unicellular Algae. Dr. Th. M. Fries, 

 who has endeavored to construct a system based on the Gonidia, 



