128 PHOTOSYNTHESIS 



scientific principles to a large scale industrial undertaking. In some 

 cases the experiments were carried out in glasshouses during the 

 winter with no measurements of the intensity and duration of the light. 

 Under these conditions it is not surprising that an atmosphere enriched 

 in carbon dioxide produced only a very slight increase or even deleterious 

 efifects. Thus, for instance, Tjebbes and Uphof ''^^ who carried out ex- 

 periments in greenhouses in December found that air enriched with car- 

 bon dioxide produced an effect only by the aid of electric light. Similarly, 

 when total growth or crop yield are taken as a criterion, careful atten- 

 tion must be given the questions relating to soil, such as mineral nutrients, 

 aeration, etc. 



Among the first to study the effect of enriching the atmosphere with 

 carbon dioxide was Demoussy."^ He used glass chambers of about one 

 cubic meter. The control plants were exposed to an atmosphere of nor- 

 mal tarbon dioxide-content while others were in an atmosphere of 0.15- 

 0.18 per cent. After two months the plants in the enriched atmosphere 

 were cut and weighed; they were 122-262 per cent or an average of 157.6 

 per cent in excess of the control plants. The increased yields of the plants 

 grown in the enriched atmosphere were not, however, directly proportional 

 to the carbon dioxide-concentration ; also different plants vary greatly in 

 the increases shown. 



TABLE 22 



Effect of Increased Carbon Dioxide-Concentration on Fresh-Weight Yield. 



(Results of Lundegardh.) 



CO2 — House Control House Excess 



Cucumbers— shoots 1.807 Kg. 0.890 Kg. 0.917 Kg. = 103% 



—fruits 25.879 " 15.187 " 10.692 " = 74 



Tomatoes— shoots 2.700 " 1.310 " 1.390 " =124 



—fruits 1.210 " 1.120 " 0.090 " = 8 



Bean-fruits 7.080 " 3.343 " 2>.7Z7 " =112 



Total 38.676 " 21.850 " 16.826 " = 77% 



Mean CO^content 0.065% 0.043% 0.22% =51% 



The recent results obtained by Lundegardh ^^^ in Sweden give a good 

 idea of the effect of carbon dioxide fertilization. The experiments were 

 carried out in glasshouses, the carbon dioxide was continuously injected 

 and the plants grew for ten weeks. Carbon dioxide detenninations were 

 made daily. In Table 22 are given some of Lundegardh's results in terms 

 of the fresh weight of the different plants. It would have been of greater 

 value if the results had also been calculated on the basis of dry weight. 



Similar experiments have been carried out on a larger scale in the 

 open field.^^^ Here the carbon dioxide, taken from cylinders or blast- 



"• Tjebbes and Uphof, LandiiK Jahrb., 56, 313 (1921). 



"'Demoussy, Compt. rend.. 139, 883 (1904). 



"' Lundegardh, "Der Kreislauf der Kohlensaure in der Natur.," p. 127. 



"• Lundegardh, 1. c, p. 135. Bornemann, 1. c, p. 85. 



