324 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, 
Fic. 288. 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 (py) 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 82 bushels per acre was 
