67 



fruits often have a hole in the center. The rim is usually rather 

 smooth and thin. Spores undivided, colorless, 5 to 8 by 4 to 5 

 microns. 



Cetraria lacunosa usually rises higher from the holdfast than 

 its close relatives (discussed under C. ciliaris), but resembles 

 them so closely that several points should be checked over. 

 Hairs on the margin would make it C. ciliaris if narrow-lobed, 

 or if broad-lobed, Parmelia perforata, a yellow under surface 

 C. juniperina, white soredia on the margins C. glauca or a 

 Parmelia, stalks and lobes all narrower than 5 mm. C. steno- 

 phylla. Other common lichens with conspicuous net-like pat- 

 tern of wrinkling are Parmelia saxatilis and P. sulcata (Group 

 6) Sticta pulmonaria and S. sylvatica (Group 7), both larger 

 and much less upright. 



Cetraria stenophylla. Slender Shield Lichen. 



Also called C. lacunosa var. stenophylla. Though differing 

 from C. lacunosa in nothing except the narrow lobes, typical 

 specimens are so distinct in appearance that they would be 

 taken for a wholly different lichen. No one has attempted to 

 say just how narrow C. lacunosa must be before it is C. steno- 

 phylla, so let us say arbitrarily that no stalk, branch or lobe of 

 C. stenophylla should be anywhere wider than 5 mm. 



Forms which appear to be C. stenophylla sometimes show 

 characters belonging to C. glauca, such as white dusty (soredi- 

 ate) margins, or coral-like growth. For these Tuckerman named 

 also a var. stenophylla for C. glauca, but his solution is not 

 satisfactory. The truth is, lichens do not always divide sharply 

 into their different forms, but have intermediates in astonishing 

 variety. Certain names therefore must be applied arbitrarily 

 and with slightly indefinite limits, if we are to name these 

 highly variable plants at all. 



Cetraria glauca. Pale Shield Lichen. 



Less common than related species, but to be looked for in 

 similar places, on living trees or dead wood. The character for 

 which it is named, a bluish gray (glaucous) color, appears also 

 in C. lacunosa, which it resembles in many ways. Tufts may be 

 10 cm. or more across, but do not commonly rise more than 

 about 2 cm. from the foothold. Lobes may be 2 or 3 cm. broad 



