DIV. II 



PHYSIOLOGY 



271 



weight and of the carbon dioxide formed show that the latter does 

 not account completely for the former ; a part of the dry substance 

 must thus have been transformed into water. 



The volume of air does not under all circumstances remain 

 unchanged by the respiration of the plant ; the carbon dioxide pro- 

 duced is not always equal in 

 volume to the oxygen which dis- 

 appears. Small deviations from 

 this ratio occur in all plants, 

 and considerable ones in, for 

 instance, the germination of fatty 

 seeds, and in the leaves of cer- 

 tain succulent plants (Crassu- 

 laceae). This is connected 

 with the fact that in these seeds 

 fats, which are much poorer in 

 oxygen than carbohydrates, are 

 used in respiration ; and that 

 in the Crassulaceae certain 

 organic acids are produced from 

 carbohydrates instead of carbon 

 dioxide and water. In other 

 plants also similar acids, though 

 not in so great amount, are 

 formed. They probably arise 

 mainly in the respiratory pro- 

 cess, but may also be produced 

 in constructive metabolism. 



In the germination of fatty seeds 

 far more oxygen is absorbed than 

 carbon dioxide is given off ; this may 

 go so far that in the first days in the 

 dark, in spite of continual respiration, 

 an increase in the dry weight takes FlG - 254. Experiment to demonstrate respiration 



place. The respiratory quotient is 



,, , ,, ,-r < i 



thus less than 1. Most of the oxygen 



is used in the transformation of fats, 

 which are poor in oxygen, into carbo- 

 hydrates, and only a'small proportion 

 is used in respiration. 



In the Crassulaceae a large proportion of the carbohydrate is changed into 

 organic acids in the process of respiration. The oxidation is thus incomplete ; 

 it does not lead to the formation of C0 2 , so that less of this gas is formed than the 

 amount of oxygen absorbed would lead us to expect. The respiratory quotient is 

 less than 1. This peculiar respiratory process which is connected with an accumu- 

 lation of acids in the cell sap, as can be recognised by the taste, is not without 

 ecological significance for succulent plants. The acids formed (especially malic and 

 oxalic acids) give off C0 2 in the light. This can be again employed in assimilation, 



inver ^ *"*, ( S '" P* rtia '\f ed , with 

 flowers which are held in place by the plug of 

 cotton (r) Owing to the absorption of the 



carbon dioxide exhaled in respiration by the 

 solution of caustic potash (K), the mercury (Q) 

 rises iu the neck of the flask - < After XOLL -) 



