104 Development and Activities of Roots of Crop Plants. 



pare with those at the beginning of the experiment. Great care was exer- 

 cised to secure thoroughly representative composite samples for nitrate 

 analysis. A small amount of toluene was added at once to the sample in the 

 air-tight jars to stop bacterial action. 



Nitrates were determined by the reduction method, using Devarda's alloy 

 and the method proposed by Whiting, Schoonover, and Richmond (1920). 

 The results of these analyses, together with the data on root extent and water- 

 loss, are summarized in table 37. Final analyses for nitrates were made only 

 in those fertilized soil layers into which the roots extended. 



Table 37 —Loss of water and nitrates 1 from November 4, 1920, to March 12, 1921. 



Con- 

 tainer. 



Depth. 



Water-content. 



Nitrates, p. p. m. 



Root development. 



Nov. 4. 



Mar. 12. 



ra 

 O 



! Nov. 4. 



Mar. 12. 



Loss. 





feet. 



p. ct. 



p. ct. 



p. ct. 









A few roots extended 3 or 4 



No. 1 . . 



to 1 



25.8 



12.6 



13 .2 



393.3 



199.4 



193.9 



1 to 2 



25.1 



21.2 



3.9 









inches into third foot. 





2 to 3 



23.6 



21.4 



2.2 











IN . Z . . 



ft +n 1 

 U TO I 



24.8 



15.9 



8.9 



390.0 



165.3 



224.7 



A few roots extended 1 or 2 



1 to 2 



26.5 



21.9 



4.6 









inches into third foot. 



No. 3. . 



to 1 



24.5 



15.4 



9.1 









All roots confined to first 2 feet. 





1 to 2 



24.4 



18.9 



5.5 



394.2 



239^4 



154.8 





No. 4. . 



to 1 



26.5 



16.7 



9.8 









Roots evenly distributed, in 





1 to 2 



26.3 



22.7 



3.6 



399.7 



139.6 



260.1 



first 2 feet only. 



No. 5'. 



to 1 



27.1 



20.5 



6.6 









A few roots penetrated 4 to 6 



1 to 2 



29.7 



27.0 



2.7 









inches into second foot. 



No. 6. . 



to 1 



25.1 



18.7 



6.4 









Roots evenly distributed in 



1 to 2 



26.5 



23.8 



2.7 









first 2 feet only. 



No. 7. . 



to 1 



25.8 



17.6 



8.2 









Very few roots below 1.8 feet. 





1 to 2 



26.9 



23.3 



3.6 











No. 8. . 



to 1 



25.9 



19.1 



6.8 









Very few roots below 1.8 feet. 





1 to 2 



27.1 



22.1 



5.0 









Best root development; evenly 



No. 9. . 



to 1 



25.6 



17.4 



8.2 



392.3 



142.4 



249.9 



1 to 2 



25.7 



23.2 



2.5 



397.8 



165.2 



232.6 



distributed in first and second 





2 to 3 



24.6 



22.3 



2.3 



395.7 



39.8 



355.9 



foot and quite abundant to 



















2.5-foot level. 



No. 10. 



to 1 



27.9 



17.9 



10.0 



399.4 



85.4 



314.0 



Evenly distributed in first 2 





1 to 2 



25.5 



24.2 



1.3 



397.3 



54.1 



343.2 



feet only. 



No. 11. 



to 1 



25.8 



16.7 



9.1 



24.2 



21.3 



2.9 



Roots in first 2 feet only. 





1 to 2 



32.1 



21.7 



10.4 



26.6 



11.4 



15.2 



Roots in first 2 feet only. 



No. 12. 



to 1 



24.0 



17.2 



6.8 



19.8 



42.7 



+22.9 





1 to 2 



26.5 



21.7 



4.8 



26.4 



11.3 



15.1 





1 The nitrate-content is given in parts per million of N0 3 . This includes not only the NOs 

 of the NaNOa added, but all N0 3 present in the soil when analyzed at the beginning and end 

 of the experiment respectively. 



2 This container was taken down on December 21. 



A study of table 37 shows that the roots developed only poorly; in only 

 3 of the 12 containers did they reach depths greater than 2 feet. Moreover, 

 they were scarcely more than half as abundant as in the earlier field experi- 

 ment (p. 94). These findings lead the writers to seriously doubt the value 

 of many greenhouse experiments with crop plants when the results are applied 

 to field conditions. Not infrequently the indoor environment is made still less 



