THE BREATHING OF THE PLANT 75 



cient to extend for at least ten inches on each side 

 of the V-shaped bend. The appai'atus is now made 

 air-tight. 



The level at which the liquid stands in the two arms 

 of the tube is marked with gummed paper and the 

 thermometer read. The temperature may then be 

 kept constant by means of a wet cloth. 



Now since no substance is put into the flask to 

 absorb the carbon-dioxide, it follows that there will be 

 no change in the level of the coloured liquid if the 

 amount of oxygen inspired equals the amount of 

 carbon-dioxide expired, provided always that there are 

 no other factors which nullify the conclusions arrived 

 at. If, however, the volume of oxygen taken in ex- 

 ceeds that of carbon-dioxide given out, the column of 

 coloured liquid in the tube will move towards the flask ; 

 conversely, the column of liquid will move in the 

 direction away from the flask should the volume of 

 carbon-dioxide expired exceed that of oxygen inspired. 



Observations. — For a time the level of the liquid 

 remains practically stationary. Soon, however, the 

 liquid is slowly pushed down the arm of the tube 

 which is adjacent to the flask. (It is not generally 

 possible to get the column of liquid further than the 

 bend of the tube, as the gas from the flask manages to 

 escape when the end of the column, of liquid stands at 

 the bend.) 



Inference. — It may be roughly estimated from this 

 experiment that the amount of oxygen inspired is 

 normally equal to that of carbon-dioxide expired, but 

 that, in the apparatus set up, the normal result is soon 

 falsified by the conditions of the experiment itself. 



{Note. — When seeds are germinated in a confined 

 space so that the supply of external oxygen is limited, 

 the seedlings are able to utilise the oxygen contained 

 within themselves for their respiration. This utilisation 

 of the oxygen contained within the tissues of the plant, 

 for respiratory purposes, is termed Intramolecular 

 Respiration. When mtramolecular respiration is taking 



