THE BRYOLOGIST. 



Vol. IV. Ji-LV, 1901. No. 3. 



LICHENS— CETRARIA. 



By Carolyn W. Harris. 

 (With Plate V.) 



To many lichenists the Cetrarias are the most interesting of the family, 

 Usneei, to which they belong, because of their varied thallus, in some spe- 

 cies resembling the foliaceous Parmelias, in others the fruticose Cladonias. 

 The name Cetraria is derived from Cetra, meaning an ancient Spanish shield, 

 which the apothecia are said to resemble. 



The Cetrarias are very generally distributed. They are found all over 

 the world, but are especially abundant in the northern part of America. All 

 the European species are found here, and we have several which do not occur 

 in Europe. 



Generally Cetrariaschoose trees for their substratum, but a few are found 

 on rocks and earth. Rhizoids are few or wanting, even where the thallus is 

 horizontal. Cilia are frequently present and in some species are very numer- 

 ous. Soredia are rare, so the surface of the thallus is smoother in appear- 

 ance than in the Parmelias. As they develop they become almost free from 

 the substratum and after a hard rain may be found entirely detached. 



The thallus varies from foliaceous to fruticose, the lobes are always flat- 

 tened and rather broad. Generally the thallus is more brittle than in Parme- 

 lia, owing to the greater development of the cortical or outer layer, and the 

 less cottony tissue of the medullary or inner layer of the thallus. In the as- 

 cendant varieties the thallus is compressed or channeled, in the foliaceous it 

 is expanded and leaf-like. In color it varies, is bright yellow, greenish yel- 

 low or straw color, olive, brown, and even black. It is smooth on the under 



side. 



The apothecia are medium to large in size, they are marginal or submar- 

 ginal, the disk colored differently from the thallus. They are attached ob- 

 liquely to the ends of the lobes of the thallus. In some species the apothecia 

 are very rare, in others they are very abundant. The disk is thin, somewhat 

 crenate or torn, ranging in color from light chestnut to dark reddish brown. 

 In shape the apothecia are shield-like, but in some species become nearly 

 round. They are flatter, less cup-shaped than in Parmelia. 



Cktraria lacunosa, Ach. (Plate V. 5.)— Thallus foliaceous, the lobes 

 rounded and deeply lacunose, giving a pitted or wrinkled appearance. The 

 margins are crenate, yet smooth. Above it is a light pearl color, sometimes 

 with a slate colored tinge. When young it is white below, growing darker 

 with age; is easily detached from the substratum. 



liij-The April number was issued Apiil i6th. 



