190 



cia of some parasitic fungus ; these apothecia take their origin 

 just above the lower cortical layer ; as growth proceeds the cortical 

 layer is pushed outward and finally ruptures, allowing the rather 

 large black apothecia to protrude ; the spores of the parasite are ob- 

 long, elliptical, colorless, two to four-celled. Most works on lichens 

 refer to the apothecia as " warty outgrowths on the lower surface of 

 the thallus." Further critical study is necessary to find the true 

 morphological and physiological relationship of parasite to host ; in- 

 cidentally it may be mentioned that careful sectioning does not reveal 

 the structural union between host and parasite ; also that the same 

 parasite seems to occur constantly, so that the question might arise 

 which are the true apothecia of Endocarpon miniatum^ or whether 

 both forms of apothecia belong to parasitic fungi. 



As already mentioned, the thallus is quite thick ; the upper and 

 lower cortical layers are well developed ; the algae (Pleurococcus 

 vulgaris} are situated in a semicortical tissue just below the upper 

 cortical layer; the algal cells, which are larger and more irregular in 

 shape than those in Dermatocarpon or Verrucaria, seem to occur 

 within the hyphal cells. No haustoria occur, since none are needed. 

 The products of assimilation pass through the algal and fungal cell- 

 walls by direct osmosis. The medullary hyphae are much branched 

 and comparatively short-celled, forming a rather close mesh-work. 



The apothecia are very numerous, small, and wholly immersed in 

 the thallus ; they open by minute pores through which the spores 

 escape. The paraphyses, spore-sacs and spores are in all respects 

 similar to those of Verrucaria. The representatives of the genus 

 seem to be more or less cosmopolitan, but E. miniatum is by far the 

 most common in the territory ; they occur upon the soil, rocks and 

 the bark of trees. 



PLATE 60. 



ENDOCARPON MINIATUM (L.) Schaer. 



1. Thallus natural size. 



2. Section of apothecium. 



3. Section of thallus. 



4. Spore-sac with spores. 



5. Spores. 



6. Algae enclosed by hyphal cells. 



