98 



THE GUIDE TO NATURE 



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BEARD MOSS (USNEA BARBATA). 



A typically fruticose lichen showing apothecia. Quite 



cosmopolitan but variable in form, size and color. 



sac-fungi, because they form their 

 spores in little sac-like structures. The 

 fungi are dependent upon the algae for 

 their organic food, and the algae are 

 protected by the fungi against loss of 

 moisture, and supply to them certain 

 necessary chemicals — a life relation- 

 ship for mutual benefit ; one supplies 

 what the other lacks, making it pos- 

 sible for two organisms to thrive where 

 neither could exist alone. As a result 

 of this partnership, the lichens are 

 wonderfully successful in the struggle 

 for existence. 



We must not confuse this mutual is- 

 tic relationship with parasitism. In that 

 there is also an intimate biological re- 

 lationship, but one organism (the host) 

 is injuriously affected, while the other 

 (the guest) is benefitted. The host 

 plant always thrives better without the 

 parasite, as in the case of the oak and 

 the mistletoe. 



These plants exist in three general 

 types or forms, fruticose, foliose and 

 crustose. The fruticose are more or 

 less branched and filamentous. The 

 widely distributed beard moss (Usnea 

 barbata) on trees, on oaks especially 

 and less commonly on posts and 

 fences,, is typically fruticose. The foli- 

 ose (leaf-like) are thin, papery and 

 fiat, and are rather loosely attached to 

 the bark. They are also found on 

 rocks and fences. Iceland moss ob- 

 tainable in drug stores is an example. 

 The crustose appear to be mere dis- 

 colorations. 



Lichens are indefinitely perennial. 

 It is probable that most of these on 

 large mountain rocks, or on aged trees, 

 are hundreds of years old. In the 

 reindeer moss of the tundra there is a 

 continuous growth at the top, while 

 the basal portions are as constantly 

 dying. 



The growth of many is extremely 

 slow, some taking years to arrive at 

 the spore bearing stage. One variety 

 has been known to grow for forty-five 

 years before producing the spore bear- 

 ing structures. 



Any bit of lichen will develop into 

 a new plant provided the part includes 

 both partners. In fact a lichen dried 

 so thoroughly that it may be pow- 

 dered, will renew its activity as an in- 

 definite number of plants, if the pow- 

 der is scattered in a suitable place and 

 kept moist. Furthermore there are 

 special propagative organs called se- 

 redia, minute bodies composed of both 

 alga and fungus and usually formed 

 along the edges of the thallus. To the 

 naked eye these clusters appear as 

 slightly raised specks, or as a white 

 fringe. The individual soredia compos- 

 ing these clusters are too small to be 

 seen by the naked eye. Other propaga- 

 tive structures are the apothecia, small 

 cup-shaped or dome-shaped growths 

 about a quarter of an inch in diameter, 

 and generally slightly raised, occurring 

 on the surface in the foliose forms, and 

 on the ends of the branches in the 

 fruticose. In the lichen known as red 

 cup moss, the bright red spots are the 

 apothecia. These tiny cups belong to 

 the fungal portion. 



The following are a few of the more 

 interesting species with a brief refer- 

 ence to their real or supposed eco- 

 nomic value. 



No lichen has been of greater in- 



