125 



The great bulk of the podetium consists of hyphal cells extending 

 for the mest part in a longitudinal direction. The hyphae are less 

 closely united than in the mechanical tissue of PiJophoron. There is 

 no line of demarcation between the outer and inner portion, and the 

 tissue becomes gradually less firm toward the interior. The center 

 is, however, never hollow nor is the tissue as loose as in Pilophoron. 



The apothecia are terminal, of medium size, somewhat globose, 

 or distinctly flattened. The thecium and upper portion of the para- 

 physes is brown in color ; the hypothecium is colorless and consists 

 of a hyphal network with considerably gelatinized cell-walls ; the 

 depth of the thecium is quite variable ; in S. coralloides the para- 

 physes and spore-sacs are very short. The spores are spindle-shap- 

 ed or acicular, colorless, usually four-celled. 



Stereocaulon is somewhat northern in its range. It also extends 

 south in mountainous regions, occurring principally upon rocks. 



PLATE 12. 

 STEREOCAULON CORALLOIDES Fr. 



1. Part of plant natural size. 



2. Portion of branch bearing apothecia. 



3. Section of apothecium. 



a, thecium ; b, hypothecium ; c, gelatinous hyphal tissue. 



4. Longitudinal radial section of thallus. 



a, portion of thalloicl wart; b, external loose network of hvphae ; c, 

 inner mechanical tissue of longitudinal hvphae. 



5. Spore-sac with spores and paraph vses. 

 a, gelatinous portion of spore-sac. 



6. Spores. 



7. Algae. 



4. CLADONIA Hoff. Deutsch. Flora Crypt. 114. 1795. 



This is one of the largest groups of lichens and its study is fraught 

 with considerable difficulty owing to the extreme variability in form 

 associated with a great uniformity in the development of the tissue- 

 elements. 



The primary or horizontal thallus is usually foliose ; in some of 

 the lower forms it is crustaceous or warty, more or less lobed and 

 ascending. Numerous thallus-lobes which retain a uniform size 

 grow from the substratum and all ascend at about the same angle ; 

 owing to this uniformity in the size and form of the primary thallus it 



