34 OUTLINES OF FORESTRY. 



some, but that such experiments succeeded in 

 some cases is undoubtedly true. 



For example, in densely-wooded countries, where 

 the ground is thickly covered with trees, the light 

 and heat of the sun are so thoroughly expended 

 in maintaining such growth that no other forms 

 of plant life occur. Let, however, some of the 

 trees be removed, so that the light and heat of 

 the sun may reach the ground, and the seeds that 

 were there, possibly during the centuries that the 

 forest covered it, at once spring into active life. 

 Here all the conditions except sufficient light and 

 heat were present, and yet the germs slumbered. 



That the Sahara desert was once, in certain 

 portions, if not in all parts, well watered, is 

 attested by the presence of the wadys, or deserted 

 river-valleys. That the soil of the desert contains 

 a liberal supply of numerous plant germs, is shown 

 by the fact that, on the successful sinking of an 

 artesian well, the appearance of the water is in- 

 variably attended by the appearance of a flora 

 often containing peculiar species of plants. Here 

 the light, heat, and soil were all present, and yet 

 the germs slumbered for want of moisture. 



The boring of artesian springs, or the digging 

 of cellars or other excavations, by bringing to the 



