320 



PART III. THE CLASSIFICATION OF PLANTS. 



the Lichen which bears the reproductive organs. From the nature of these 

 organs the Lichen-Fungi have been found to belong chiefly to the discomyce- 

 tous and pyrenornycetous Ascomycetes, but a few are basidiomycetous, belong- 

 ing to the orders Hymenomycetes and Gasteromycetes. The Lichens may be 



classified as follows, according 

 to the nature of the Fungus. 



I. Ascolichenes (Ascomycer 

 tous Lichens). 



1. Discolichenes (Discomy- 



cetous Lichens), e.g. 

 Parmelia, Collema, 

 Usnea, Peltigera, 

 Sticta, Cladonia, etc., 

 Lecidea, Graphis. 



2. Pyreuolichenes (Pyre- 



nomycetousLichens), 

 e.g. Pertusaha, Ephe- 

 be, Lichina, Verru- 

 caria, Endocarpon, 

 etc. 



II. Basidiolichenes (Basidio- 

 mycetous Lichens). 

 Lichens), Cora, Dictyonema, 



FIG. 226. Section of a spermogonium of Ana* 

 ptychia ciliaris : sp the aperture at the surface ; 

 c cortex, and m medullary portion, of the thallus ; 

 g layer of algal cells. (After Strasburger.) 



1. Hymenolichenes (Hymenomycetous 



Ehipidonema, Laudatea. 



2. Gasterolichenes (Gasteromycetous Lichens), Emericella. 



The reproductive organs of the Ascolichenes are sterigmata, producing 

 spermatia, contained in spermogonia (Fig. 226) ; archicarps (in the order 

 Collemaceae), differentiated into a coiled ascogonium and a multicellular pro- 

 jecting trichogyne ; and ascocarps, which are either apothecia (discomyce- 



tous) or perithecia (pyrenomy- 

 cetous) ; the archicarp, appar- 



ently after fertilisation (see p . 



298), gives rise to filaments 

 which form the hymenial layer 

 (consisting of asci and para- 

 physes) of the apothecium, and 

 outgrowths from the adjacent 

 vegetative hyphae form the wall 

 (excipulum] of the apothecium. 

 In the fructification of the 

 Basidiolichenes there is a hy- 

 menial layer consisting of para- 

 physes and basidia, the latter 

 bearing apical sterigmata, on 

 each of which a basidiogoni- 

 dium is produced by terminal 



FIG. 227. A-D Soredia of Usnea barlata. A A 

 simple soredium, consisting of an algal cell covered 

 with a web of hyphae. B A soredium, in which the 

 algal cell has multiplied by division. C A group 

 of simple soredia, resulting from the penetration of 

 the hyphse between the algal cells. D K Germin- 

 ating soredia : the hyphae are forming a growing- 



point, and the algal cells are multiplying. 

 Sachs.) 



(Alter 



abstriction. 

 Lichens are also reproduced 



