308 



BOTANY. 



to completely evaporate before placing in the moist chamber. By tak- 

 ing precautions to keep out moulds, by supplying the moist chamber with 

 air passed through one or two plugs of cotton-wool, he succeeded in 

 continuing the growth of the hyphae for three months, at the end of 

 which time the algse were surrounded by a good number of branches 



FIG. 213. 



Fig. MZ.Usnfabarbafa, nat. size, a, a, apothecia ; f, disk by which it is attached 

 to the bark of a tree. After Sachs. 

 Fig. 213. Stiota pulmonacea, nat. size. , a, apothecia. After Sachs. 



of the hyphae, many of which had firmly attached themselves to the 

 cells of the algae. 



(c) The classification of lichens is by no means settled. 



The arrangement which is followed in this country ia that of Profes- 

 sor Tuckerman.* He divides the order into five tribes, as follows: 



TRIBE I. PARMELIACEI. 



Apothecia rounded, open, scutelliforin, contained in a thalline exciple. 



Family 1. Usneei. Rocce.Ua, Ramalina, Dactylina, Cetraria, Ever- 

 Jiia, Uanea (Fig. 212), Alec o>ia. Roccella <inctoria nnd other species of 

 the genus furnish the dye known as orchil, and chemical test " litmus." 

 Cetraria islandica, the Iceland moss, is used botli as a food and a medi- 



* Edw. Tuckerman : " Genera Lichenum ; An Arrangement of North 

 American Lichens," 1872, 



