PRODUCTS OF RESPIRATION 73 



bourhood of unity ; on the other hand, if fat be so consumed, 

 the ratio will be less than unity. To take actual figures : the 

 value of CO 2 /O 2 for germinating oats, which are starch-con- 

 taining, and for germinating mustard, which contain fat, de- 

 termined by physical methods was found to be '99 and '92 

 respectively. 



Although carbon dioxide represents a final product of 

 the complete respiration of carbon compounds, other sub- 

 stances may be end products if physiological combustion be 

 incomplete. Succulent plants provide instances of this ; 

 members of the Crassulaceae do not give off carbon dioxide 

 when first placed in darkness although the absorption of 

 oxygen is active. There is, however, an accumulation of 

 organic acids, malic and oxalic, and it is not until these 

 have accumulated in relatively large quantities that carbon 

 dioxide is evolved as in a normal plant* The peculiar meta- 

 bolism of these plants is generally associated with and ex- 

 plained by their massive structure rendering the movement 

 of gases a relatively slow process. In other words, the 

 catabolism stops at an organic acid stage which forms a 

 reserve of carbon dioxide which is rendered available for 

 carbon assimilation when the acids are decomposed under 

 photosynthetic conditions. There is thus a conservation of 

 carbon dioxide. Comparable phenomena occur in bacteria 

 under certain conditions, the formation of acids being a well- 

 known occurrence in their oxidative activities. 



Of other products of respiration, carbon monoxide has 

 been described by Langdon and Gailey in the pneumatocysts 

 of Nereocystis Luetkeana*[ a unique example as far as is 

 known. The bladders contain an atmosphere of nitrogen, 

 oxygen, carbon monoxide, but no carbon dioxide. An 

 analysis of the gaseous contents of over a thousand of these 

 floats showed the carbon monoxide to vary from I to 1 2 per 

 cent by volume, whilst the oxygen ranged from 15 to 25 per 

 cent. Only when oxygen is present does carbon monoxide 

 form in the bladders ; if the oxygen be replaced by nitrogen 

 or hydrogen, no carbon monoxide results. The gas is pro- 

 duced naturally both by day and by night but it is not formed 



*See Nicolas: "Compt. rend.," 1918, 167, 131. 



f Langdon: "Journ. Amer. Chem. Soc.," 1917, 39, 149; Langdon and 

 Gailey : " Bot. Gaz.," 1920, 70, 230. 



