172 GUIDE TO THE STUDY OF LICHENS. 



1. Conotrema urceolatum. Epiphloeodal portion of 

 thallus evenly spreading, thin, whitish. Apothecia 

 urn-shaped when fully matured, partially enclosed 

 by thallus. Disk of a waxy color, margin black. 

 Spores typical of genus, 140/x, X V- 



^. Thelotrema. 



As in Conotrema, the thallus is rudimentary and 

 partly hypophloeodal. The algag are Chroolepus. 



The apothecia are characteristic. They resemble a 

 miniature volcanic crater. They are numerous and 

 quite uniformly scattered over the thallus. Upon ex- 

 amining the opening at the top the whitish perithecium 

 can be seen within ; that is, the perithecium becomes 

 separated from the more inflexible cone. A whitish, 

 waxy coloration pervades the entire plant. 



The spores are large, colorless, multilocular, spindle- 

 shaped, with a thick rugose spore-wall. 



There is a considerable number of species which 

 occur upon trees in the warmer latitudes. 



1. Thelotrema lepadinum. Thallus thin, uniformly 

 spreading, smooth, white to cream color. Apothecia 

 usually numerous, conical, immersed, with a circular 

 opening through which the light-colored perithecium 

 can be seen. Spores large, colorless, spindle-shaped, 

 12 to 16 transverse septa, and a few longitudinal septa 

 at the middle. Spore-wall thick, rugose, 51^ X 13/x. 



5, Gyrostomum. 



Thallus rudimentary. Apothecia quite small and 

 semi-globose. Both thallus and apothecia begin their 



