FUNGI. 263 



distinguished by a singular parasitism. Their hosts are Algae, which grow normally in 

 damp places but not actually in water, and belong, moreover, to very various groups 

 (rarely Confervaccce, frequently Chroococcaceae and Nostocacete, more often Palmellaceae 

 sometimes Chroolepus). The Fungi themselves (Lichen-forming Fungi) are not found 

 in any other form than as parasites on Algae; while the Algae which are attacked 

 by them, and which, when combined with the Fungus, are called Gonidla, are known 

 in the free condition without the Fungus. When the species attacked by the Lichen- 

 fungus is a filamentous Alga, and the development of the hyphal tissue is only moderate 

 (as in Ephebe and Coenogonium), the true state of the case is at once clear ; and as 

 Lichens of this kind have become better known, the suspicion has frequently arisen that 

 they are in fact only Algae infested by Fungi. In the Gollemaceae also attention has 

 frequently been drawn to the identity of the gonidia with the moniliform filaments of 

 Nostocaceae ; but in this case the nourishing Alga usually undergoes considerable changes 

 of habit, at least in its external contour, from the influence of the parasitic Fungus, 

 like Euphorbia Cyparissias from its parasitic iEcidium. But the greater number of 

 Lichen-fungi prefer as hosts the Chroococcaceae and Palmellaceae which grow as stains 

 and incrustations on damp ground, the bark of trees, and stones. The separate cells 

 and groups of cells of these Algae become so involved by the tissue of the Fungus, 

 that they are at last only interspersed here and there in the dense hyphal tissue, 

 or appear in it as a peculiar layer (the gonidial layer). The growth and multiplica- 

 tion of these Algae, which thus become entirely enclosed by their parasites, is not 

 hindered, but their development is disturbed in other ways. When, however, they 

 are freed from their enclosing Fungus-tissue, their normal development proceeds, and 

 in a few cases even the formation of zoospores takes place in them, a fact first observed 

 by Famintzin and Baranctzky, but incorrectly explained. It is to Schwendener's know- 

 ledge of the facts, the result of researches extending over many years, that the correct 

 interpretation is due in these cases of the relationship borne by the Lichen-forming 

 Fungus to the gonidia, /. e. to the Alga which it attacks \ 



After these preliminary remarks the following description will be intelligible to the 

 beginner. It is transferred, with but slight alterations, from the first edition of this book. 

 We will consider first the Lichen as a whole, as it comes under observation, the 

 nourishing Alga being distinguished as an elemental form of the thallus under the name 

 Gonidia; and will afterwards discuss the nature of the nourishing Algae more in detail. 



The Thallus of Lichens is commonly developed in the form of incrustations which 

 cover stones and the bark of trees, or penetrate between the lamellae of the epidermis 

 of woody plants, and then expose only the receptacles above the surface. These Crus- 

 taccous Lichens, as they are termed, have become so completely united in their growth 



were obtained when the spores of Biatora musconnn were sown upon Protococcus. Spores of 

 Parmelia sown separately ramified much less and developed no chlorophyll ; Protococcus, on the 

 other hand, during the same period remained unchanged and put out no hyphse. Tulasne, however, 

 sowed the spores of Lichens and believed that he twice detected the formation of gonidia upon the 

 hyph?e (Ann. des Sci Nat. 1852, XVII, pp. 96-98). De Bary indeed described the green gonidium 

 as originating by the expansion of a short lateral branch of the hypha into a globular cell, which 

 is shut off by a septum and assumes a green colour; once formed, it increases independently by 

 division, and a number of the gonidia eventually lie without stipites in the interstices of the 

 Lichen-tissue (Morph. u. Phys. der Pilze, pp. 258, 263-265). Berkeley also believes that the 

 gonidia originate from the hyphce, having had ' a good opportunity of ascertaining their development 

 from the threads of the mycelium in specimens developed within' the vessels of pine wood' (Introd. 

 to Crypt. Bot. p. 373). For a careful resume ol all the recent literature of the subject by Archer, 

 see Quart. Journ. Micr. Sc. 1873, p. 217. In this country Bentham has criticised Schwendener's 

 view (Address to Linn. Soc. May 23, 1873), and Thwaites and Berkeley have also expressed their 

 dissent (Gard. Chron. 1873, p. 1341). — Ed.] 



^ A few additional historical notes will be found at the end of this section. 



