Introductory y 



up under their sheltering shade. But these latter are 

 mown down as fast as they grow by the hungry cattle 

 of the Arabs ; and even the trees do not escape, for 

 the goat devours the seedlings whenever it has the 

 opportunity, and the camel will bite through thorny 

 branches as thick as the finger, and unfortunately it 

 has a particular liking for the twigs, leaves and seed- 

 pods of the Acacia ; so that between them, the tree of 

 the desert has but little chance. If only they were left 

 undisturbed for a few years these spots would be 

 covered with groves, which would gradually extend 

 where now little can grow but the foxglove and 

 colocynth. 



Still, even now, these deserts cannot be called bare, 

 though their crops are scanty. As we have said before, 

 the labourers on the great farm do not allow any 

 surface to be bare, if they can help it, and they work 

 as if it were their one object to grow as many crops as 

 possible. The very snow-fields and ice-fields are not 

 allowed to lie idle, for there is soil even here, and it 

 must not be wasted. 



Dust, meteoric dust from the higher regions beyond 

 our atmosphere, is constantly falling all over the earth, 

 to the amount, it is believed, of more than 500,000 tons 

 every year; and though, being scattered evenly over 

 the whole surface, it must be spread very thin indeed ; 

 still, where there is no other mineral matter, as on the 

 snow and ice-fields of the Arctic regions, it is quite 

 perceptible, and it is enough for the growth of such 

 humble vegetables as the * Red Snow,' which in 

 summer covers the white surface with a flush of rose- 

 colour many miles in extent. Nor are this and other 

 similar minute plants grown to no purpose. These 



