FAMILIES AND GENERA 339 



Thallus non-corticate below. 



Apothecia terminal i. *Heterodea Nyl. 



Apothecia superficial 2. *Physcidia Tuck. 



Thallus spongy below 3. *Anzia Stizenb. 



Thallus corticate below. 



Asci poly-spored 4. Candelaria Massal. 



Asci 8-spored. 



Spermatia acrogenous 5. Parmeliopsis Nyl. 



Spermatia pleurogenous. 



Apothecia superficial 5. Parmelia Ach. 



Apothecia lateral. 



Apothecia on upper surface 7. Cetraria Ach. 



Apothecia on lower surface 8. *Nephromopsis Miill.-Arg. 



XLVII. USNEACEAE 



This also is afamiliarfamily of lichens, Usnea darl?ata the "bearded moss" 

 being one of the first lichens noted and chronicled. Algal cells Protococ- 

 caceae. Structure radiate, the upright or pendulous habit characteristic of 

 the family securing all-round illumination. Special adaptations of the cortex 

 or of the internal tissues have been evolved to strengthen the thallus against 

 the strains incidental to their habit of growth as they are attached in 

 nearly all cases by one point only, by a special sheath, or by penetrating 

 hold-fasts. 



Apothecia are superficial or marginal and sometimes shortly stalked ; 

 spores are simple or variously septate. 



Ramalina and Usnea, the most numerous, are cosmopolitan genera; 

 Akctoria inhabits northern or hilly regions. 



The genus Evernia, also cosmopolitan, represents a transition between 

 foliose and fruticose types; the fronds of the two species, though strap- 

 shaped and generally upright, are dorsiventral and stratose, the gonidia 

 for the most part lying beneath one surface; the other (lower) surface is 

 either white or very dark-coloured. Everniopsis, formed of thin branching 

 strap-shaped fronds, is also dorsiventral. 



A number of genera, Thamnolia, Siphula, etc. are of podetia-like structure, 

 generally growing in swards. Several of them have been classified with 

 Cladoniae, but they lack the double thallus. One of these, Endocena, a 

 sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was 

 classified by Hue' along with Siphula; recently he has transferred it to his 

 family Polycaulionaceae^ based on Polycauliona regale {Placodium frustu- 

 lostmi Darbish.), and allied to Placodium Sect. Thamnoma^. In recent studies 

 Hue has laid most stress on thalline characters. He places the new family 

 between "Ramalinaceae" and " Alectoriaceae." Dactylina arctica is a common 

 Arctic soil-lichen. 



' Hue 1892. ^ Hue 1914. ' Tuckerman 1872, p. 107. 



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