TISSUES OF LICHENS. 



^53 



reproductive cells (spores) are produced, 

 differentiated, however, as in the fruits 

 of Phanerogams, at the ripening of fruc- 

 tification. The previously slimy internal 

 hyphal tissue then dries up completely, 

 and the dense portions containing the 

 spores then appear as peculiar organs, 

 which remain free in the cavity of the 

 entire Fungus : this now, enclosed by 

 the firm epidermal layer, has some- 

 what the shape of an ordinary flower- 

 pot. 



The fruticose Lichen, represented 

 in Fig. 163, may serve as a second ex- 

 ample of hyphal tissue. The Lichens 

 are, as we now know, true Fungi, 

 which have the peculiar habit of en- 

 closing in their tissue their host-plants 

 which contain chlorophyll (that is small 

 Algae) without interfering with their re- 

 production : these appear in owe draw- 

 ing as dark granules. These elements, 

 serviceable, it is true, to the proper 

 body of the Lichen, but foreign in 

 other respects, behave within the hy- 

 phal tissue just as if they only con- 

 stituted a special layer of tissue, cor- 

 responding to the assimilating paren- 

 chyma of a green plant ; and this to 

 such an extent, that up to sixteen years 

 ago, when De Bary first perceived the 

 true nature of Lichens, these en- 

 closed Algae were considered as a 

 special form of tissue of the body of the 

 Lichen itself. Apart, however, trom 

 these remarkable facts. Fig. 163 shows 

 with all requisite clearness the diflFeren- 

 tiation of the hyphal tissue into three 

 systems. The outermost of these may 

 be at once designated epidermal tissue ; 

 and in the interior is a strand separated 

 from the epidermal tissue. Thus again 

 we meet with the three forms, which we 

 have to regard as the most rudimentary 

 indication of the three typical systems of 

 tissue of the higher plants. 



The tissues in this case are only fully 



FIG, 163. — t/sitect l/ariafa, 3. fruticose 'Lichen, ^ optical longi- 

 tudinal section of a thin branch, in potash ; H transversa section of a 

 tliicker branch ; jr the ^/j^is (so-called Gonidia) ; r epidermal layer ; 

 m fundamental tissue; x the axial strand. 



FIG. 164. — Haiymeda opuntia. A a shoot — natural size ; B longi- 

 tudinal section of a segment (slightly magnified) perpendicular to the 

 plane of the paper. The segments of .^ are flat. 



