3i8 



THALLOPHFTES, 



Rye, or of other nearly allied grasses, Kiihn states that the sphacelia arises from them, 

 and the cycle of development is thus completed. 



(6) Lichens^ From the researches of Schwendener'^, there can no longer be any 

 doubt that the Lichens are true Fungi belonging to the Ascomycetes (Discomycetes 

 and Pyrenomycetes), but 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 Gonfervaceae, frequently Chroococcaceae and Nostocaceae, 

 more often Palmellaceae, sometimes Chroolepideae). The Fungi themselves (Lichen- 

 forming Fungi) are not found in any other form than as parasites on Algas ; while the 

 Algae which are attacked by them, and which, when combined with the Fungus, are 

 called Gonidia, 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 Collemaceae 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 

 jEcidium. 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 special layer (the gonidial layer). 

 The growth and multiplication 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 zoogonidia takes place in them, 



* Tulasne, Memoire pour servir a I'histoire organographique et physiologique des Lichens 

 (Annales des Sci. Nat. 3rd series, vol. XVII). — Schwendener, Untersuchungen iiber den Flechten- 

 thallus (in Nageli's Beitrage zur w^issensch. Botanik. i860 and 1862. — Ditto, Laub- u. Gallertflechten 

 (Nageli's Beitrage zur wissensch. Botanik. 1868). — Ditto, Flora, 1872, nos. 11-15. — Stahl, Beit. z. 

 Entwickel.-Gesch. der Flechten, 1877. [Quart. Journ. Micr. Sc. 1873, p. 235, and 1878, pp. 



144.438-] 



"^ [The views of Schwendener have been corroborated by Bornet in an elaborate memoir pub- 

 lished in the Ann. des Sci. Nat. 1873, vol. XVII. He also put them to a synthetical test by sowing 

 the spores of Parmelia pariethia upon Protococcus. About the fifteenth day the hyphse were well 

 developed and ramified. Wherever they met isolated cells of Protococcus or groups of them, 

 they attached themselves either directly or by means of a lateral branch. They did this to the 

 Protococcus only, neglecting altogether the other bodies which were mixed with it. Similar results 

 were obtained when the spores of Biatora muscorum 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 

 hyphse (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 hyphse. 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 of 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 Lin, Soc. May 23, 1873), and Thwaites and Berkeley have also expressed their 

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



