336 



BOTANICAL GAZETTE 



[APRIL 



The root of each set of three that had the best tap root was 

 photographed, and is shown in figs. 1-5. The left hand root in each 

 figure was grown in soil that did not receive carbon dioxide treat- 

 ment; the middle one shows the residual effects of the 8 hours; 

 and the right hand one shows the effects of 24 hours of gas treat- 

 ments. With no gas treatment the roots of plants grown in manure 

 tend to resemble those in which carbon dioxide gas was applied to 

 the soil. This is confirmation of the statement made in the previous 

 paper, namely, that "the results obtained in these experiments lead 

 to the belief that the carbon dioxide content of garden soils is some- 



TABLE I 

 Residual effects of carbon dioxide gas additions to soil on development of tap 



roots of Lactuca sativa 



Previous fertilizer 

 treatments* 



NO CARBON DIOXIDE 

 GAS TREATMENT 



Nothing 



Five tons dry manure J . . 

 Complete fertilizer 



(single application)!. . 

 Ten tons dry manure . . . 

 Complete fertilizer 



(double application) . . 



Average 



Length 

 (in inches) 



Distance to 

 first curve 

 (in inches) 



•05 



4-9 

 4-4 



4.0 



3-of 

 5° 



2-3 

 3-4 



1-7 



8 hours' carbon 

 dioxide treatment 



DAILY 



Length 

 (in inches) 



3 



4 



4 

 3 



3 



4-7 



3.1 



4 



7 

 7 



5 

 9 



Distance to 

 first curve 

 (in inches) 



i-3 

 1.6 



1-7 



2.0 



1.9 



24 hours' carbon 

 dioxide treatment 



1-7 



DAILY 



Fig. no. 



Length 

 (in inches) 



D istance to 

 first curve 

 (in inches) 





2.8 



4-5 



4-2 



i-9 

 3° 



0.9 

 0.9 



0.9 



I 



2 



3 



4 



5 



3-3 



1.1 



1 





* In addition nitrogen was applied in ammonium nitrate on four dates at rate equivalent to 50 pounds sod 

 nitrate per 2,000,000 pounds soil. 



t All figures are the average for three plants. % Application per 2,000,000 pounds of soil. n i, 03 . 



§Made from dried blood, dicalcium phosphate, and potassium chloride containing equal nitrogen, pu 

 phorus, and potassium; nitrogen equal to one-third that in the 5 tons of dry manure. 



times detrimental to the root development of some of the plants 

 growing in the garden." 



These residual effects of carbon dioxide additions to soil obtained 

 over 9 months after the treatments were discontinued were un- 

 expected, as the soil had been removed from the pots and mixed, 

 and all water lost by evaporation added subterraneously. The 

 explanation is not easy. The data are reported as a contribution to 

 the knowledge of root growth, and it is hoped that it may help some 

 workers in explaining odd tropic phenomena or throw some light 

 on what is known as "soil toxicity." 



Mellon School of Industrial Research 



Pittsburgh, Pa. 



