178 HUMBLE FAMILIES IN GRAY. 



them. They are the corals of the air ocean, as it 

 were, built up slowly by the atoms of moisture 

 and light, and heat, and are faithful in their duty 

 in making soil and preparing it for the growth of 

 higher plants. Pluck a specimen of this Cladonia 

 pungens, growing so commonly in shallows on the 

 ledges in pale, dense clumps. It is as slender 

 and fragile as spun glass when dry. How easily 

 it is separated from the earth, because it has 

 hardly the suggestion of a root. The horizontal 

 thallus, or mat of scale-like leaves, seen in many 

 other species, is here entirely absent. Into what 

 a curious entanglement of branches has this tuft 

 of hollow stalks been developed ! It is a compact 

 thyrsus of branch tubes, grown together, a minia- 

 ture lichen banyan tree, without roots. The axils 

 or armpits of the branches are perforated as if 

 with pins, and the tips of the numerous little 

 forks and teeth at the extremities of the branch- 

 lets are colored brown. These are the sterile 

 summits. The fruitful ones, not so abundant and 

 usually found on separate tufts, are arranged at 

 the tips of certain stalks, in little clusters or 

 cymes. A pale, ash-colored, more loosely-branched 

 kind, with curved or drooping summits, and also a 

 species called Cladonia raccmosa, with greener 

 ramified stalks, thickly beset with scales, is fre- 

 quently mingled with this lichen. All of them 

 are found, I believe, in high northern latitudes, 



