2U2 



PLANT PHYSIOLOGY 



able. On the basis of the above statement, fertilization with 

 carbon dioxide has been applied during the past few years with a 

 view toward obtaining higher yields. This was done first in 

 greenhouses and afterward under the conditions of field experi- 

 mentation, where carbon dioxide was conducted to the field by 

 pipes. This method, of course, is practical only in the neighbor- 

 hood of large factories, which throw into the air immense quan- 

 tities of carbon dioxide. The Krupp factories in Essen, for 

 instance, produce as much as- 3,000,000 kg. of carbon dioxide 

 per day. Especially favorable results have been obtained in 



S 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 

 *^ CO2 Confen+ of Air, per cenf 



Fig. 61. — Dependence of assimilation of pine needles on the carbon dioxide con- 

 tent of the air {ajter StMfdt, from Lundegardh) . 



greenhouses, where, with insufficient aeration, often not even 

 traces of carbon dioxide can be found in the air during the 

 day. When this gas is introduced artificially, often a 100 to 

 150 per cent increase in yield has been secured. The rapid 

 development of the plants in hotbeds underlaid with manure 

 seems to be due not only to the higher temperature thus pro- 

 duced but also to the abundant supply of carbon dioxide. 



Under natural conditions, plants obtain carbon dioxide not 

 only from the atmosphere but also from the soil. Owing to the 

 processes of decomposition of the organic substances in the soil 

 by different microorganisms, carbon dioxide is liberated. Diffus- 

 ing from the soil in the lower layers of the atmosphere, it is caught 

 by the leaves of the plants. According to the calculations of 



