CHAPTER XLVIII. 

 STRUGGLE FOR OCCUPATION OF LAND. 



466. Retention of made soil. — In the struggle of plants for 

 existence, there are a number of species which stand ready to 

 rush in where new opportunities present themselves by changed 

 conditions, or by newly made soil. The permanent drainage of 

 ponds or marshes brings changed conditions, and the flora there 

 undergoes remarkable transformations. The deposits of the 

 washings of streams in protected places along the shores, or at 

 their mouths, where deltas or lateral plateaus are made by the 

 accumulations of soil scoured off the banks of the stream, or 

 washed off the fields during rains, make new ground. With 

 such banks of newly made_ ground are deposited seeds carried 

 along with the soil, or dropped there by the wind, by birds, or 

 other agencies of seed distribution. 



467. Vegetation of sand dunes. — Along the sandy beaches 

 of lakes, or of the ocean, drift piles of the fine sand are formed, 

 which often are moved onward by the wind. The surface par- 

 ticles are moved onward to the leeward of the drift, and so on. 

 The form and location of the sand dune gradually changes. 

 Such drifts sometimes slowly but surely march along over soil 

 where a rich vegetation grows, and over valuable land. Even 

 on these sand dunes there are certain plants which can gain a 

 foothold and grow. When a sufficient number obtain a foot- 

 hold in such places they retain the sand and prevent the move- 

 ment of the dune. 



468. Reforestation of lands. — When by the action of fire or 

 wind, or through the agency of man, portions of forests are 



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