]^3 ^''^* °" *^® mountain top 



important ingredient of all fertile soil, supplying food and 

 moisture for the plants which grow in it. 



Each larger herb or shrub adds its contribution to the 

 humus. After thousands of years a great pine may be grow- 

 ing where nothing had grown before and where nothing 

 could ever have grown if the lichen, which asks so little, 

 had not come first. This process has taken place countless 

 times in the past. It is following the same sequence of 

 events today in countless places and one need only look 

 about in any mountain region to see the various stages. 

 Where the pine is was once a lichen. Where the lichen is 

 may some day, perhaps millennia hence, be a pine. 



It would be a rash man who would undertake to es- 

 timate very closely the age of one of the lichens growing 

 on an Arizona peak or anywhere else. Unfortunately they 

 produce no annual rings to be counted. They cannot even 

 be dated by the new carbon isotope method because that 

 method reveals only how long ago a thing died, not for 

 how long it has been living. But one thing is certain. 

 Many lichens grow very, very slowly and they must have 

 taken a long time to reach the size attained by some in- 

 dividuals. 



It is commonly said that the giant redwoods of Cali- 

 fornia are the most ancient individual living organisms, 

 and they are old enough. A fallen giant whose rings can 

 be counted had lived for a little more than three thousand 

 years. A still standing tree is almost certainly quite a bit 

 older. But it has been suggested with some show of rea- 

 son that certain very large individual hchens may be even 

 older. Perhaps not the majestic tree but a humble lichen 

 has lived through more history than any other growing 

 thing. 



