190 



On the Exhaustion of Soils, 



from week to week, to note the ratio existing between the vege- 

 table matter formed, and the inorganic matter abstracted from 

 the soil. In the early part of the experiment the rate of growth 

 was very regular, so that by weighing a few plants from time to 

 time the increase in weight of the roots every day might be readily 

 ascertained. The experiment was commenced in July when the roots 

 weighed about 3 oz. each, and were then increasing at the rate of 

 nearly an ounce a day ; this rate of increase appeared to continue 

 pretty regularly, for about six weeks, after which the plants grew far 

 less regularly, an effect in part due to the unsettled state of the 

 weather. The following Table shows the composition of the roots 

 examined, during fifteen consecutive weeks, and also the composi- 

 tion of the seeds previous to germination. 



The results of this series of experiments exhibit less regularity 

 than might have been expected ; the conclusions to be drawn 

 from them as regards the degree of exhaustion are arranged in the 

 following Table. 



