200 



algal branches remain without hyphae. It must also be remembered 

 that careful examination with the aid of a good microscope is abso- 

 lutely necessary to determine whether the plant under consideration 

 is Sh-ostp/wi^ puh'inatus or Ephcbc pnbescens. The hyphae are fur- 

 thermore quite slender and devoid of any special characteristics of 

 color and form. 



The difficulty is further increased by the fact that apothecia are 

 very rare. So far I have been unable to detect any apothecia in 

 the numerous specimens of E. pnbescens examined. Sperm agonia 

 are, however, very frequently present ; these appear as minute glis- 

 tening pustules on the sides of the thallus, finally opening on the ex- 

 terior by a minute pore. 



This group of lichens is evidently low in the scale of development 

 because there are practically no changes in structure or function as 

 the result of the symbiotic association. The lichen occurs in the same 

 position as the alga and, as already indicated, has practically under- 

 gone no change in form. 



The apothecia are said to occur within the algal tissue in the older 

 branches ; these apothecia-bearing branches are recognized by a knot- 

 ted swollen appearance, and they remain covered by the algal tissue 

 until maturity, when an opening is formed to allow the escape of 

 spores. 



The Ephcbcs occur upon rock and soil in wet places or where 

 there is running or dripping water ; their distribution seems to be 

 through the temperate and tropical zones. 



PLATE 70. 



EPHEBE PUBESCENS Fr. 



1. Natural size. 



2. Branch of thallus magnified; a, apothecia ; b, spermagonia. 



3. Section of thallus-branch and a spermagonium. 



4. Section through a younger portion of a thallus-branch ; c, formation 

 of a new branch. 



5. Spore-sac with spores (after Crombie). 



6. Spores (after Crombie). 



7. Sterigmata. 



8. Spermatia. 



2. LECOTHECIUM Trev. ; Kbr. Syst. Lich. Ger., 398. 1855. 

 The position of this genus is rather difficult to determine. The 



