GROUPS OF PLANTS. 



41 



duces, like many other Lichens, disk-hke or cup-shaped bodies at 

 various places on the surface of the thallus, which are known as 

 APOTHECiA and which may be regarded as exposed or open asco- 

 carps. The inner surface of the apothecia is lined with a number 

 of asci as well as sterile cells, the former giving rise to ascospores. 



Fig. 26. Different types of Lichens, i , Cladonia gracilis var. verticillata showing long, 

 slender, upright thalli or podetia; 2, Cladonia cornucopioides, the disk at the summit of a 

 podetium being bright scarlet; 3, Cladonia fimbriatawith long, slender podetia; 4, Cladonia 

 rangiferina a very abundant, wiry, fruticose Lichen; 5, Cetraria islandica; 6, a specimen 

 of Evernia vulpina found growing on Pinus Lambertiana in California, known as the Wolf's 

 moss, and showing the large, disk-like, terminal apothecia bearing thalloid filaments. 



Economic Uses of Lichens. — A number of the Lichens are 

 used in medicine, as several species of Cetraria, Pertusaria com- 

 munis, Physcia parietina, Sticta pulmonacea, Evernia furfuracea. 



