Soil-Binders 41 



away. Its bare, exposed surface is washed and wasted by 

 the rain, dried and blown away by the wind; for there is 

 nothing" to protect it from either, to begin with. But this 

 state of things does not last long. There is always plenty 

 of seed floating in the air, ready to sow itself on any bare 

 space it can find; so that in two or three years' time the 

 embankment is overgrown with grass, whose roots are so 

 matted together that further shifting of the soil is to a 

 large extent prevented. 



Of course, where seed is sown even before the soil is 

 made, as we have seen in the case of lichens, there the 

 mold as it is formed is kept in place and protected, and is 

 able to deepen undisturbed. But where sand has been 

 heaped together by the wind, or mud deposited on the 

 coast, there something is needed to give it firmness, or 

 else it will be dispersed again. 



The sandhills on the plains of Venezuela, for example, 

 are still constantly moving to and fro, here to-day and 

 there to-morrow, except in one district, where they have 

 been consolidated into a low range of permanent hills 

 by a curious grass with tall, cutting, sword-edged blades, 

 which grows so closely and with such rapidity that any 

 paths made by travelers are quite covered up and destroyed 

 by it in a few days. 



The plants which are most useful for this work of bind- 

 ing the soil and giving it its first firmness are those which, 

 besides growing quickly, also send out especially long 

 roots, runners, or underground stems, often miscalled 

 roots, which are pegged down at frequent intervals by real 

 roots, much in the same way as the thatcher binds down 

 the straw on the rick-top. The couch-grass and others 

 have long underground stems of this sort, as the gardener 



