LICHENS. 



391 



•will be necessary, however, in order to make clear to the reader the true state of 

 affairs in connection with these remarkable plants, to refer very briefly to their 

 anatomical structure. It has long been known that the body of the Lichen consists of 

 two entirely different forins of tissue : of typical fungus tissue, which also produces 

 the organs of fructification, and of cells containing chlorophyll, mostly spheroidal or of 

 some other shape, which present an unmistakeable similarity to simpler forms of 

 Algse. In the year 1 864 De Bary first pointed out that these gonidia, in a certain group" 

 of Lichens at least (the gelatinous Lichens), may be true Algae, which, interweaved by 

 the hyphae of true Fungi, serve to nourish the latter. This idea, suggested by Da" 

 Bary, was generalised later by Schwendener; and by means of a series of experi- 

 mental works by Baranetzky, Reess, and Stahl, complete certainty was attained that all 

 Lichens are, as a matter of fact, nothing other than Fungi belonging to the subdivision 

 of the Ascomycetes, which are accus- 

 tomed to weave themselves around 

 Algae, usually microscopically small, 

 and entirely to envelope them, so 

 that an organism compounded of a 

 Fungus and an Alga arises. Figure 

 250 shows, according to Bornet, a 

 few examples of the ways and means 

 by which the germinal filaments of 

 the corresponding Lichen-fungus lay 

 hold of and weave themselves around 

 Algae. The Fungi also germinate, 

 it is true, in the absence of the 

 Algae, but they then perish; and a 

 Lichen-body only comes into ex- 

 istence when the germinating Fungi 

 are able sufficiently early to become 

 united with the Algae with which 

 they are adapted to form a Lichen, 

 since each Lichen-fungus, according 

 to its specific nature, is confined to 

 certain forms of Algae. 



It has been demonstrated, particularly by Bornet and Stahl, that in consequence 

 of the union of Fungus and Alga the vigour of both is promoted. Without going 

 further into detail, it is only necessary to mention that the Algae imprisoned by the 



Fig. s4^Sti£ia fuliffiitasa ; transverse section throu£:h the foli- 

 aceous thallus. o upper. « lower epidermal layer : m nt tissue of matted 

 fungus hyphae : r r roots ; eg cells of the Alga dividing and increasing 

 (highly magnifiedK 



up in the text. He put aside all at once the matters referred to above as hitherto obscure and 

 doubtful. Moreover, direct proof was forthcoming by the method of synthesis: i. e. by the union 

 of definite autonomous Algse with suitable Fungi a designed Lichen-thallns was produced. 

 Reess and Stahl have now shown that this may be accomplished with comparative ease by observing 

 certain precautions.' 



More details on the Lichens are found in my ' Lehrhuch,' Aufl. IV, pp. 319-330. An interesting 

 general description also by Reess, ' ff birdie Natur der Flechten' (Berlin, Habel). The highly 

 interesting work of Stahl's referred to is • Beitrage zur Entwickelungsgeschichte der FUchten,' Heft 2 

 (Leipzig, 1877, Felix). Among the finest and most instructive works is that of Ed. Bornet, 

 ' Reiherches sur les Gonidies des Lichens^ Ann. des sc. nat. 5' ser. Tome XVII, i« cahier. 



