158 



THE ROTHAMSTED EXPEEIMENTS. 



Growth 

 of root- 

 nodules. 



ripe. Each of the eight descriptions of plant was grown in 

 sand (with the plant ash), watered with the extract from a 

 rich soil ; also in a mixture of two parts rich garden-soil and 

 one part of sand. The pits, with their plants, were exposed 

 to the open air, but protected from heavy rain. 



In the sand the infection was comparatively local and 

 limited, but some of the nodules developed to a great size on 

 the roots of the weak plants so grown. In the rich soil the 

 infection was much more general over the whole area of the 

 roots, the nodules were much more numerous, but generally 

 very much smaller. Eventually the nodules were picked off 

 the roots, counted, weighed, and the dry substance and the 

 nitrogen in them determined. 



Among the annuals the peas, and among the plants of 

 longer life the sainfoin, showed perhaps the most normal 

 growth ; and the results given in Table 46 afford interesting 

 illustrations. 



TABLE 46. — Experiments at Rothamsted on the Fixation op 

 Free Nitrogen. Plants grown in pits, and taken up at successive 

 periods, 1890-91. 1. In sand (with ash), microbe-seeded ; 2. In a 

 mixture of rich soil and sand. 



Date of 

 taking up. 



Number 



of 

 plants. 



Approxi- 

 mate 

 number. 



Nodules. 



Weight, 

 dried at 

 100° C. 



Nitrogen. 



In dry. Actual 



PEAS, 1890. 



fist period 

 In sand-! 2nd h 

 (.3rd „ 



( 1st period 

 In soil < 2nd „ 

 { 3rd m 



Aug. 4 



Sept. 24 



Nov. 29 



Aug. 5 



Sept. 26 



Dec. 2 



grams. 

 0.0152 

 0.0185 

 0.0034 



0.0373 

 0.0474 

 0.0447 



SAINFOIN, 1890-91. 



'1st period 



ld i3rd I! 



.4th „ 



In soil 



1st period 

 2nd „ 

 3rd „ 

 4th „ 



Dec. 10, '90 

 May 15, '91 

 June 12, '91 

 Sept. 11, '91 



Dec. 13, '90 

 May 15, '91 

 June 12, '91 

 Sept. 14, '91 



0.0112 

 0.0133 

 0.0641 

 0.2085 



0.0025 

 0.0937 

 0.0412 

 0.2331 



