THE VOICE OF THE DESERT 



162 



other species used as a food in southwest Asia in times of 

 famine may have been the manna of the Old Testament. 

 But the hchen s greatest service — one that man was long 

 unaware of — was paving the way for all other plants. 



Imagine a granite peak which some cataclysm has thrust 

 up into the cold air. It is hard, and smooth and dead. No 

 root could penetrate it or find nourishment if it did. Frost 

 might crack and flake the surface in time, but it would 

 still be incapable of sustaining even the humblest weed. 



Presently the wind carries aloft the spore of a lichen 

 which comes to rest on the bare surface. A little moisture 

 is all it requires. It can cling to the bare surface without 

 roots. It can hve on the infinitesimal traces of ammonia 

 and other chemicals in the air. It carpets the bare rock 

 with a thin film of hving matter. Some sorts can hve even 

 on glass and they have been knov^n to damage church win- 

 dows by eating their way into them! 



Presently the lichen on the mountain top dies. But 

 where life has been, other forms of hf e can estabhsh them- 

 selves. Perhaps the spore of a moss comes next and is able 

 to exist because of the less-than-paper-thick coating of or- 

 ganic matter left by the lichen. When the moss dies that 

 coating will be considerably thicker. Some less humble 

 plant — not improbably a fern — can grow there now.' After 

 it will come something else still larger. 



Meanwhile, frost and the mild acids of the growing 

 things have begun to break dowm the rock. It cracks and 

 crumbles. Into the little pockets formed here and there 

 the rain washes the remains of the lichen, the moss 

 and the fern. They are mixed with the gravel and sand of 

 the disintegrating granite. They are "humus," that all- 



