SYNTHESIS, STORAGE AND BREAKDOWN 



135 



By a suitable elaboration of this arrangement the amount of carbon dioxide 

 evolved could be determined and an index of the rate of respiration so ob- 

 tained. It could be shown that respiration quickens with increasing tem- 

 perature until levels are reached at which the cell-structure is adversely 

 affected ; also that actively-growing material such as germinating seeds 

 respire more quickly than mature or dormant parts of plants. This observation 

 is indicative of a close connection between respiration and growth. If by 

 any treatment respiration is checked, growth is correspondingly depressed. 

 Practical advantage of this has been taken in the storage of fruit and vegetables. 

 By storing these in an atmosphere which is initially rich in carbon dioxide, 

 respiration is reduced, the development and over-ripening of the material 

 is slowed down, while the growth of micro-organisms is likewise discouraged. 



Fig. 87. 



Arrangement for demonstrating gaseous interchange in Respiration, a, shows an 

 earlier stage of the experiment ; b, a later stage. See Text. 



Another instructive experiment dealing with the respiratory 

 interchange of plants is shown in Fig. 87. A quantity of flower-buds 

 or of germinating seeds is placed in a long-necked flask, which is then 

 fixed with the neck projecting downwards into a dish of mercury. 

 A strong solution of caustic potash is then floated above the mercury 

 in the neck. The potash serves to absorb the carbon dioxide which 

 we have seen to be produced by the respiring material. At the same 

 time the mercury is observed to rise up the neck of the flask (see 

 Fig. 87, b), indicating that some part of the original atmosphere of 

 the flask has been absorbed by the respiring material. Actually it 

 is the oxygen that is so absorbed, as is indicated by the observation 

 that the mercury continues to rise until the volume of the gas within 

 the flask has been reduced by about one-fifth. 



