NO. 15 AERIAL FERTILIZATION OF WHEAT JOHNSTON 9 



produced, and (6) slightly delayed the time of heading. The weight 

 per grain was practically the same as that of the controls even in the 

 experiment in which phosphorous and potassium fertilizers were 

 added at time of heading. 



Great differences in growth were obtained in the plot experiments 

 between the enclosed plants and those grown in the open. The en- 

 closed plants were larger, heavier, and more succulent, and the weight 

 per grain was somewhat greater. In the pot experiment the plants in 

 the open culture (no. 5) grew better than those of the corresponding 

 control (no. 4). There appears to be some evidence, since this pot 

 experiment, of a toxic effect of cellulose acetate. If this is true, it 

 may account for the poorer growth of the plants enclosed in the 

 cellulose acetate cylinders. It would appear that the higher humidity 

 within the enclosed plots was beneficial to these plants. The evidence, 

 however, is not conclusive, since the temperature was also higher 

 within than without the enclosures. 



The aerial fertilization of plants with carbon dioxide raises a num- 

 ber of interesting questions. Many of these can be answered, however, 

 by laboratory experiments under controlled conditions. The practical 

 application of this type of fertilization in field experiments and the 

 supply of carbon dioxide in sufficient amounts for practical field 

 work are still unsolved problems, in spite of the work that has been 

 done. Even its application to greenhouse culture requires the utmost 

 precaution. The escape of the gas mixture into a greenhouse is not 

 sufficient in itself, but a recirculating system, as noted by Owen {4) 

 aids materially toward obtaining uniform distribution. While experi- 

 ments in which carbon dioxide is used as an aerial fertilizer are of 

 important scientific value, the practical application of this type of 

 fertilizer in commercial work is far from being satisfactory, although 

 its application to greenhouse culture appears to be most promising. 



REFERENCES 



(i) Arthur, John M., Guthrie, John D., and Newell, John M. 

 1930. Some effects of artificial climates on the growth and chemical composi- 

 tion of plants. Amer. Journ. Bot., vol. 17, pp. 416-482. 



(2) CuMMiNGs, M. B., and Jones, C. H. 



1918. The aerial fertilization of plants with carbon dioxide. Vermont Agr. 

 Exp. Stat. Bull. 211, pp. 1-56. 



(3) Hoover, W. H., Johnston, Earl S., and Brackett, F. S. 



1933- Carbon dioxide assimilation in a higher plant. Smithsonian Misc. Coll., 

 vol. 87, no. 16, pp. 1-19. 



(4) Owen, Owen. 



1923. Carbon dioxide investigations. Exp. and Res. Sta., Nursery and Market 

 Garden Industries' Development Soc, Ltd., 9th Ann. Rep., pp. 82-94. 



