548 SOILS. 



is more than will be tolerated by the ordinary culture-plants, 

 must be judged either from the accompanying plants, or by 

 experiment or analysis. 



Relative Tolerance of the Different Species. The follow- 

 kig table shows in systematic order the tolerance of the several 

 plants discussed above, for the different salts, so far as the 

 data available permit. The column marked optimum shows 

 under what proportions of salts the plants grew in about equal 

 luxuriance, therefore under, apparently, the most favorable 

 conditions. Both above and below the proportions mentioned 

 in that column, the luxuriance (size) and (usually) the 

 abundance of the plants was less; showing that while excess- 

 ive amounts of salts depressed their welfare, yet they also 

 suffered when the proportions dropped below a certain point. 

 Whether this was partly or wholly the result of competition 

 with other plants, is an unsettled question. 



