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i. TRYPETHELIUM Spreng. Kennt. d. Gewachse, 3: 350. 1804. 



This group takes the same position in the family that Mycocali- 

 cinm does in the Caliciaceae. Some of the representatives are very 

 doubtful lichens. In all of the species occurring in the territory the 

 thallus is very rudimentary and entirely hypophloeodal. Careful 

 sectioning and searching is necessary to detect any algae {Chroo- 

 lepus umbrina), which occur in small clusters distributed about the 

 base of the apothecia. The thallus can not be said to have any 

 structure. There is simply a meagre hyphal network, continuous 

 with the hyphae of the apothecium, which encloses the algae ; the 

 filaments are slender, much branched and much contorted. Tucker- 

 man and others describe the structure and macroscopic appearance of 

 the thallus, which plainly shows that these authors had in mind the 

 secondary color-changes in the substratum (bark), and not the thallus. 

 The network of hyphae holding the algae occurs in the intercellular 

 spaces of the bark. Neither of the symbionts ever penetrate the 

 intact cork cells. The chemical changes causing the modifications 

 in color of the bark have not been satisfactorily explained, but they 

 are doubtless clue to acids secreted by the lichen. 



The apothecia are likewise entirely hypophloeodal. They occur 

 in clusters of five to forty or even more. Each apothecium is, how- 

 ever, entirely free from the neighboring ones and may be con- 

 sidered as an individual belonging to the colony ; the outlines of 

 these colonies are very irregular. The apothecium is globular in 

 form and simple in structure. The dark to black hypothecium and 

 proper exciple (perithecium) at first entirely enclose the thecium 

 consisting of long, simple, slender, soft, more or less gelatinous 

 paraphyses and the spore-sacs. As the apothecia grow they push up 

 the superimposed layer of bark, producing a warty appearance of the 

 surface. At maturity the excipular opening (ostiole) widens more 

 and more ; finally a small pore-like opening is also formed in the 

 layer of cork which allows the spores to escape. The paraphyses 

 are highly hygroscopic and there is little doubt that they play an rrn- 

 portant part in forcing up the layer of bark as well as in ejecting 

 the spores. The covering of bark performs the function of the cor- 

 tical layers in the higher lichens, that is, it forms a mechanical 

 protection for the rudimentary thallus and the young growing apo- 

 thecia. The corky covering immediately above the apothecia is of 

 a dark rusty color, which gradually fades into the brownish or 

 greenish color of the area over the thallus. 



