GROUP I. THALLOPHYTA : LICHENTS. 



305 



mycelium gives rise to dark-coloured compact strands of hyphse, 

 of the pseudo-parenchymatous structure characteristic of sclerotia ; 

 but they are peculiar in possessing continued apical growth, and 

 by this means they soon become long filaments, known as Rhizo- 

 morpha. It is in this way that the Fungus spreads from tree to 

 tree : the Rhizomorpha-filaments grow underground from the roots 

 of an infected tree to those of a healthy tree (usually a Conifer) ; 

 it penetrates into them and spreads in the tissues external to the 

 wood in the form of a white fan-shaped mycelium. The compound 

 sporophores (Agaricus melleus) are borne either on the subter- 

 ranean Rhizomorpha-filaments, or on the parasitic mycelium ; in 

 either case they come to the surface. 



The Basidiomycetes are classified as follows : 



Series I. PROTOBASIDIOMYCETES : basidia multicellular. four-celled, each 

 cell bearing a spore ; simple conidiophores generally present. Principal 

 genera 5 Pilacre, Auricularia, Tremella, Exidia. 



Series II. Autobasidiomycetes : basidia unicellular ; simple conidio- 

 phores in some forms. 



This series consists of the two orders Hymenomycetes and Gasteromy- 

 cetes, which are distinguished by the facb that in the former the hymenium 

 is exposed before the maturity of the lasidiospores, whereas in the latter, 

 the hymenium either remains altogether enclosed in the tissue, or is 

 exposed only after the spores are ripe. 



The principal genera of Hymenomycetes are, Clavaria, Hydnum, Poly- 

 porus, Agaricus (Mushrooms) 5 and of Gasteromycetes, Lycoperdon (Puff- 

 ball), Ehizopogon, Cyathus, Geaster, Phallus. 



Subsidiary Group. LICHENES. A Lichen consists of a Fungus 

 and an Alga, living in intimate connexion^ and both contributing to 

 their mutual welfare that 

 is,symbiotically (see p. 275). 



The Lichen-Fungus has al- 

 ways a mycelioid body, and 

 is the constituent of the 

 Lichen which bears the re- 

 productive organs. From 

 the nature of these organs 

 the Lichen-Fungi have been 

 found to belong chiefly to 

 the discomycetous and py- 

 renomycetous Ascomycetes, 



but a few are basidiomy- 



, , . FIG. 185. Section of a spermogonium of Ana- 



cetous, belonging to the ptMcWa Cl ,^ 8: sp the ape P rtnre K at the 8urface ; 



orders Hymenomycetes and c cortex> and TO medullary portion, of the thallus ; 



Gasteromycetas. g layer of algal cells. (After Strasburger.) 



M.B. X 



