RESIDUAL EFFECTS OF CARBON DIOXIDE GAS ADDI- 

 TIONS TO SOIL ON ROOTS OF LACTUCA SAT1VA 1 



H. A. Noyes AND J. H. Weghorst 



(with five figures) 



Variations in the development of roots of plants, when carbon 

 dioxide gas is added subterraneously, have been described and 

 reported in a previous paper. 2 The plants subjected to the carbon 

 dioxide gas treatments were Capsicum annuum abreviatum, Lactuca 

 sativa, Raphanus sativus, and Phaseolus vulgaris. The last three spe- 

 cies were grown in the same soil, with fertilizer and manure treat- 

 ments in addition to the check treatment already reported upon. 



The treatment of the soil in the pots subsequent to the removal 

 of the Phaseolus vulgaris plants in June 191 7 was as follows. The 

 soil in each pot was emptied into a large pan, thoroughly mixed, 

 and returned to the pot. The water content was brought up to 

 optimum, and one seedling of Lycopersicum esculentum placed in 

 each pot. L. esculentum is considered a heavy potash feeder, and 

 the plants were grown without carbon dioxide gas treatments in an 

 endeavor to ascertain through plant growth the plant food made 

 available by the previous gas treatments. The L. esculentum 

 plants were harvested in November (5 months later) , and the pots 

 kept at near optimum moisture content until February 1, when 

 they were again set to Lactuca sativa. The object of this test was 

 to discover whether, on the addition of available nitrogen (in which 

 the soil was lacking), more mineral plant food, made available by 

 the carbon dioxide treatments of the previous spring, could be 

 utilized by the growing plants. The moisture content of the soil 

 in the pots was maintained at optimum by weighing and adding 

 distilled water. Available nitrogen in the form of ammonium 

 nitrate in quantities equivalent to 50 pounds of sodium nitrate per 

 2,000,000 pounds of soil was applied (with the distilled water added) 



1 Contribution from Purdue University Agricultural Experiment Station, La 

 Fayette, Indiana. 



3 Bot. Gaz. 66:364. 1918. 

 Botanical Gazette, vol. 69] - l33 2 



