LICHENS. 



245 



vegetative body in these is best compared to the foliage-leaves of the Curled Mint, 

 with their corrugated or sinuate margins, or to those of Malva rotundifolia. It 

 may also be described as a number of lobes radiating irregularly and bifurcating 

 repeatedly, and only lightly joined to the substratum by root-like fringes, and there- 

 fore capable of being readily loosened and detached. The light-grey Parmelia 

 saxatilis, which bear brown saucer-shaped fructifications, may be taken as a repre- 

 sentative of these Foliaceous Lichens. The Fruticose Lichens are distinguished as a 

 third group in which the thallus rises from the ground in the shape of a shrub, 

 whilst the cylindrical, fistular, and ligulate stemlets, which ramify profusely, are 

 only adherent to the substratum by a very small surface at the base. With these 

 are associated the Beard Lichens, which hang down from the bark of old trees in 

 the form of pale, copiously-branched filaments. Lastly, there is a fifth group, the 



Fig. 58.— Fruticose and Foliaceous Lichens. 



1 Stereocaulon ramulosum in conjunction with Scytonema; X650. 2 Cladonia furcata with Protococcus; x950 

 s Coccocarpia molybdwa; section, x650 (after Bornet). 



Gelatinous Lichens, which when moistened look like dark, olive-green, or almost 

 black lumps of wrinkled and wavy jelly or as if composed of variously-divided 

 bands and strips packed together into little cushions. 



In the gelatinous expansions last mentioned the algal cells are arranged in 

 moniliform rows and are interwoven with the hyphal filaments of the fungus 

 throughout the entire thickness of the thallus, as in Collema pwbposum (see 

 fig. 57 2 and 57 3 ), or else they form regular ribbon-shaped double rows, interwoven 

 with few hyphae, as in JEphebe Kerneri (see fig. 57 1 ). In crustaceous, foliaceous, 

 and fruticose lichens, the algal cells constitute a disorderly heap and are crowded 

 together in the middle stratum of the thallus, where they are imbedded between 

 an upper and a lower layer of densely felted hyphal threads, as in Coccocarpia 

 molybdcea (fig. 58 3 ). 



Seeing the wide distribution of lichens it must be assumed that both partners 

 occurring in the lichen-thallus are able to range about with extraordinary ease and 

 latitude. When one observes how patches of the most various lichens are produced 

 in a few years after a landslip on the freshly-broken surfaces of the stones which 



