The Origin and Nature of Lichens 



rails, unpainted cabins, and all other hard unsightly things which 

 Nature wishes to render soft and beautiful. 



"O'er yon low wall, . . . whose rough, discordant 



stone 



Is massed to one soft gray by lichens fine 

 The tangled blackberry, crossed and recrossed, 



weaves 

 A prickly network of ensanguined leaves." 



J . R. Lowell An Indian Summer Reverie. 



Collema pulposum (nat. 

 size). A gelatinous lichen 

 with Nostoc as alga. 



The ruby-throated hummingbirds know 

 these lichens and so use them in decorating 

 their nests (Plate I) as to make it difficult to distinguish them 

 from lichen-covered knot holes. The Lungwort (Sticta pulmo- 

 naria, Colour Plate VII), so called from the resemblance of the 

 pitted surface to the surface of a lung, does not encrust the bark 

 on which it grows, but clings lightly to its support when moist 

 and curls up its under white surface when dry, to protect its 

 green surface. On the same tree with 

 the Lungwort one often finds an hepatic 

 (Porella platyphylla, Colour Plate XIV), 

 with braided strands, and a moss (Neck- 

 era pennata, Colour Plate III) creeping 

 around the tree trunk its strands in 

 parallel rows. 



On overhanging cliffs by lake or 

 stream, or on huge rocks in the forest, 

 one finds the oddest lichen of all, the 

 Rock Tripe (Colour Plate XI). When wet, 

 the velvety green shields lie flat, held by 

 a stout cord at their centres. As the air 

 around them becomes dry, the edges 

 begin to curl, bringing the soot-black 

 under surfaces to the light to form black tubes here and there 

 over the rocks. With every change in the moisture of the air 

 the Rock Tripe curls and uncurls, writhes, and twists; at 

 one time presenting its gray or green surface, at another its 

 black. This lichen is also used for food and is said to have 

 saved the life of Sir John Franklin in the Arctic seas, when he 

 was reduced to starvation. 



29 



Section of Collema pulposum to 

 show uniform distribution of 

 the alga throughout the whole 

 thickness of the thallus. 



