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INTRODUCTION TO BOTANY 



is not settled, notable experiments that have been carried 

 on at the experimental station at Harpenden, England, since 

 1848 will show the nature of some of these studies. Certain 

 crops have there been grown year after year upon the same 

 soil. A barley field which has been unfertilized since the 

 experiments began, produced, in the year 1849, a little over 

 40 bushels per acre. Each year thereafter, with no fertilization, 



FIG. 238. Effect of quality of soil on growth of roots 



The cucumber plant shown in the figure was grown in a shallow box, one end of 

 which was filled with sand and the other with rich loam. The seed was planted 

 in the sand, quite near the partition (p) of mosquito netting which separated the 

 sand from the loam. When the plant was one foot high, the earth and sand were 

 washed away and the roots sketched. Those grown in the loam weighed nine 

 times as much as those in the sand. Three eighths natural size 



barley has been grown on the same field, and the yield has 

 steadily decreased, so that during the twenty years ending with 

 1909 the average per year was less than 15 bushels per acre. 

 Another piece of ground was used for wheat, turnips, and 

 clover in rotation (with three years given to each rotation), 

 and was fertilized by the use of nitrogen and mineral fertilizers. 

 Considering only the wheat records, we have the following: 

 In the first twenty years the average yield of wheat for the 

 years in which wheat was grown was 35.3 bushels per acre ; 

 in the second period of twenty years 32 bushels per acre was 



