CLADONIA. 



265 



genera, and one especially liable to puzzle the student in the 

 determination of species. The surface of the podetium is 

 sometimes covered with a green, granulose powder (gonidia), 

 with irregular, wart-like granules, or with horizontal squa- 

 mules ; it is frequently lacunose, or it may have a carious, 

 eroded, or cancellated appearance. Sometimes the podetium 

 is divided superiorly into a number of irregular, short ra- 

 mules, which may be fertile or sterile. The scyphi are 

 usually closed by a membrane or diaphragm. The margin 

 is entire or variously divided and toothed ; sometimes it sends 

 up a number of little stalks or ramules which serve as pe- 

 dicles for the fructification. The apothecia are sometimes 

 seated on the diaphragm, on the margin of the scyphi, 

 directly or on its pedicle-like prolongations, rarely on the 

 thalline squamules, or on the curvatures of the podetium ; 

 they may be solitary or aggregate, separate or symphycar- 

 peous. Prom possessing a vertical as well as a horizontal, a 

 secondary as well as a primary, thallus, the Cladonias rank 

 among the highest typical forms of Lichens. The podetium 

 may be regarded as a modification by involution of the simple 

 thalline foliole or squamule. A similar modification of the 

 leaf frequently takes place in the Phanerogamia, as for in- 

 stance in the pitcher of the so-called Pitcher-plant. This 



