No. 4.] 



SOIL EXIIAUSTIOX. 



283 



the primitive condition and one that is more or less run out, 

 let us examine the following table. These analyses were 

 made in each case with water-free samples. 



Table alioioing the Amount of Organic Matter in Some Massachu- 

 setts Soils. 



* Practically the same as at the surface. 



The percentage of organic matter shows, as might be 

 expected, remarkable differences. Sample No. 1, which 

 approaches primitive soil, was taken from a region where 

 deforestation has not been common, and the large amount 

 of organic matter represented here is the result of years of 

 leaf-decay. The color of the surface soil is black ; at eiijht 

 inches below the surface it is only a trifle lighter. Sample 

 No. 2 presents a yellow color below the surface, on account 

 of the slight amount of organic matter present. This sam- 

 ple, which supported a growth of inferior grasses, golden- 

 rods, etc., presented a dark color only at the surface. 

 Sample No. 3 is a greenhouse soil, adapted to forcing crops. 

 These soils usually contain from eight to fifteen per cent of 

 organic matter to a depth of twelve to fifteen inches which 

 is supplied by manure and by the decay of roots. 



Those plants which have shown the greatest tendency to 

 become rare, and in most instances are only to be found 

 wdicre there is more or less of an api)roach to primitive soil 

 conditions, are the humus-loving plants, or those which 

 depend upon organic matter. Not only is the number of 

 humus-loving plants decreasing, but their former luxuriance 

 is by no means the same. Certain wild species of plants, 

 when grown in a soil similar to sample No. 1, are from one- 

 half to three times as large as those grown in soils which 



