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RADIATION BIOLOGY 



dioxide causes growth by formation of new cell matter. The conditions 

 are very similar to those found by Myers with Chlorella and permit the 

 conclusion that in nongrowing leaves nitrogen-containing compounds 

 having the average composition of amino acids appear which ought to 

 be regarded as the first identifiable assimilatory products together with 

 sugars. These nitrogenous compounds form if nitrate is present, and the 

 excess carbon dioxide assimilated is deposited in sugars. 



Table 8-3. The Assimilation of Cabbon Dioxide and Accumulated 

 Nitrate in Wheat Leaves of Different Ages 



" Computed as the equivalent amount of hexose in millimoles. 



Table 8-4. The Respiratory Breakdown of Sugar and Assimilation of 



Accumulated Nitrate in Wheat Leaves at Low Carbon Dioxide 



Content of the Air (0.07 mg/liter) 



" Initial amount about 0.150 mmole, computed as hexose. 



'' As the equivalent amount of hexose in millimoles. 



' Reassimilated or in other ways converted in non-sugar compounds. 



The fact that the respiration is independent of light is easily shown 

 by experiments with a reduced carbon dioxide content of the air [Table 

 8-4, with 0.07 mg of carbon dioxide per liter; this is close to the apparent 

 threshold value of Gabrielsen (1948), at which there is no net exchange 

 of carbon dioxide with the air]. There is a constant consumption of 

 sugar irrespective of the intensity of the illumination, whereas the assimi- 

 lation of nitrate steadily increases with the light intensity. In the dark 

 the consumed sugar is quantitatively given off as respiratory carbon 

 dioxide, but in the light it is partly withheld in the leaves as non-sugar 

 compounds. This may be due either to a true reassimilation of respira- 



