ECOLOGY OF FUNGI 8l 



(b) Upper cortical layer. 



(c) Algal layer (gonidial layer). 



(d) Medullary layer. 



(e) Lower cortical layer. 



The tegumentary layer consists of several rows of flattened hyphal 

 cells extending at right angles to the underlying cortical cells which 

 consisting of hyphal cells are pseudoparenchymatous, resembling the 

 parenchyma tissue of higher plants. The algal layer contains the 

 gonidia, or green plants, which act as hosts to the fungous hyphge. The 

 medullary layer which is thicker than the others consists of much 

 elongated hyphae forming a loosely interwoven tissue with large air 

 spaces. The lower cortical layer is pseudoparenchymatous and from its 

 lower surface rhizoids are developed. The apothecia and perithecia 

 are the fruit bodies of the ascomycetous fungi which form the lichens. 

 A vertical section through an apothecium of Sticta shows the following 

 layers: (a) the epithecium, (b) the thecium consisting of the spore 

 sacs (asci) and paraphyses, (c) the hypothecium or hyphal structure 

 immediately below the thecium, (d) upper algal layer, (e) medullary 

 layer, (/) .lower algal layer, (g) cortical layer (Fig. 26). 



Some of the fruticose lichens have a central core-like strand of hyphae 

 running through the medullary region which serves as supporting 

 mechanic tissue as in Usnea barbata. The soredia are vegetative repro- 

 ductive bodies consisting of from one to many algae surrounded by 

 continuous hyphal tissue and are common upon the upper surface and 

 margins of most of the higher lichen thalli. Among the Basidio- 

 LiCHENES basidia are formed with basidiospores on sterigmata as in 

 Cora, Dictyonema, Laudatea. 



