PRACTICAL BOTANY. 



outer layer or epidermis. Beneath the epidermis is a layer 

 of dense, colorless, fungal tissue. Below this is a layer 

 containing green cells of the algal constituents of the 

 Lichens. These green cells were formerly thought to be 

 the fructifications, and were called gonidia, which name is 



still retained. Notice 

 that the hyphse of the 

 Fungi are in close con- 

 tact with the algal cells. 

 Passing below the algal 

 layer, the fungal tissue 

 becomes looser, and the 

 interlacing, branching, 

 colorless tubular cells of 



FIG. 81. Section through the apothecmm 



of Anaptychia ciliaris. m, the algal which it is Composed 



portions; g, the gonidial portions; h, s h ow morp r l ear l v fheir 

 the hymenium; y, the subhymenial 



layer. A small portion of this apothe- fungal nature. On the 



cium may be seen more highly magni- l nwpr ;,] n f fh p QPP firm 



fied in Fig. 77. (Goebel.) L W6r S1Cle Ol tne sectlon 



the tissue passes again 



into an epidermis. In favorable places the threadlike, 

 projecting rhizines may be seen. Repeat these observa- 

 tions on sections cut from a piece of Lichen that has been 

 kept in alcohol. Keep the specimen wet with alcohol 

 while cutting the sections, and mount the sections in 

 alcohol. (Compare Fig. 80.) 



4. Cut transverse sections of the stem portion of the 

 fruticose Lichen Usnea barbata. (Fig. 79, A.) This Lichen 

 grows in abundance on old trees. It may be recognized by 

 its decidedly shrublike form, its round stem, its conspicuous 

 apothecia, which are flattened expansions of the thallus, 

 and its general bristling, bearded appearance. Mount the 

 sections in water. Observe how closely the cross section 

 of the stem of this Lichen simulates the stems of the 

 higher plants. On the outside the fungal tissue is differ- 

 entiated to resemble an epidermis ; then comes a layer of 



