PRIMITIVE SOILS 97 



table fragments and dust collect round them, and so 

 a primitive soil is built up. If the seed of a rock 

 plant should have the good fortune to come to rest 

 on such a spot, its chances are good. Some sort of 

 soil at least exists, and that not entirely free from 

 moisture. 



Sometimes Mosses play the chief part in the for- 

 mation of primitive soils, but these plants are rarely 

 the first colonisers, though often the second, where 

 some primitive soil already exists. 



A very common soil of this nature in the Alps 

 consists of little matted masses of pine-needles that 

 is, of the leaves of Pines, Spruces, or Larches. These 

 are blown for considerable distances by the wind, and 

 may come to rest in the cracks on the bare face of a 

 rock, or cling to the little knobs or irregularities of the 

 surface (Plate XLIV., Fig. 1). They form small 

 masses interlocked together, which are wonderfully 

 permanent, though not fixed to the rock face in any 

 way. They retain a considerable portion of the rain- 

 water that falls on them and collect humus and dust. 

 Thus in the end a primitive soil results. 



One of the greatest of the rock colonisers in the 

 Alps is the genus Sempervivum, the House-leek, 

 which plays a part somewhat similar to the Coltsfoot 

 with us in Britain. The House-leeks are extremely 

 interesting plants in many directions, as we hope 

 to show. 



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