THE BROWN EOOT EOT OF TOBACCO AND OTHER PLANTS 23 



The results were even more striking in 1924 than in the preceding 

 year, following, however, the same general trend. (Figs. 19 and 

 20.) The tobacco crop was poorest after timothy, followed closely 

 by tobacco after corn and after clover. The best yields followed 

 tobacco and fallow. Yields after onions, tomatoes, potatoes, and 

 beans occupied an intermediate position. Comparing the relative 

 yields with those of 1923 (Table 2) it seems apparent that the 

 injurious action following timothy, corn, and clover is increased 

 hj two years of these crops as compared with one year's cropping. 

 The single-fertilized plats are again somewhat better than the 

 double-fertilized plats, and a fairly marked falling off in yield on 

 the lime plat may be noted. 



Fig. 17. — Tobacco growing after tobacco on plat 8 at Whately, Mass., August 24, 

 1923. Compare with Figure 16 



By comparing the yields in the B series of plats, namely, those 

 following a crop of tobacco in 1923, preceded, in turn, by the re- 

 spective crops used in rotation, a remarkable recovery from the 

 brown root-rot condition, as indicated by increased yields, is evident 

 in the timothy, corn, and clover plats and to a lesser extent follow- 

 ing beans, potatoes, tomatoes, and onions, whereas in the plats 

 growing the third crop of tobacco there is no significant increase 

 over that of the preceding year. On the other hand, if we com- 

 pare the yields in the B series in 1924 with each other it is evident 

 that there is still a residual effect of the crop grown two years 

 previously, this effect being much more marked in the case of tim- 

 othy, corn, and clover than with the other crops. The yields of 

 tobacco in continuous culture and the fallow plats during 1922, 1923, 

 and 1924, indicate that no residual effect from the injurious action 

 of timothy of 1921 and preceding years existed in 1924. In other 

 words, judging by these experiments, the injurious agent apparently 

 disappears when the crops which act injuriously are kept off the 

 ground for two years. 



