128 



layer is well developed ; the internal mechanical tissue forms a 

 continuous cylinder of considerable thickness. The diameter of the 

 podetium is greater than in the majority of the Cladonias. 



The podetium is either simple or sparingly branched. It is 

 widest at the bottom, gradually tapering to a point, and presents a 

 peculiar mealy appearance on its outer surface owing to a large 

 deposit of acid crystals upon the cell-walls of the outer cortical lay- 

 ers. The color of the apothecia is a uniform greenish-grey. 



Although several authors have reported apothecia and spores, it is 

 now generally admitted that it is always sterile. After the most 

 careful examination of European and American specimens I have 

 been unable to detect the least traces of apothecia. 



Thamnolia occurs upon soil and rocks in the higher altitudes and 

 latitudes. 



PLATE 14. 

 Cladonia and Thamnolia vermicularis Ach. 



1. Thamnolia natural size. 



2. Longitudinal radial section of the podetium of Thamnolia. 



a, outer semicortical tissues ; b, algal layer ; c, inner hyphal tissue. 



3. Young primary thalli of Cladonia on a section of old bark. 



4. Portion of transverse section of the podetium of Cladonia. 



a, protective layer; b, algal layer; c, medullary layer; d, mechanic- 

 al tissue of longitudinal hyphal bundles. 



5. Cladonia verticillata Flk. 



a, apothecia upon short apothecial stalks ; b, spermagonia. 



Family 3. LECIDEACEAE. 



At present the limitations of this family are uncertain, and this is 

 particularly the case with the lower groups included in it. In gen- 

 eral it may be stated that it is often doubtful whether a given genus 

 should be placed with the Lecidiaceae, or with some other family. 

 This doubt will continue until more reliable investigations are made 

 in regard to the fungal as well as algal ancestors of the various 

 groups ; such investigations may lead to the establishment of a new 

 family or families ; the grouping here adopted is according to our 

 present knowledge of the natural relationship of the genera. 



The Lecideaceae differ from the two families preceding in the 



