288 



VEGETABLE PHYSIOLOGY 



absorption of oxygen, attended as before by an exhalation 

 of carbon dioxide, the latter having combined with the 

 potash. 



The evolution of carbon dioxide by the plant can be 

 more easily demonstrated by the use of the apparatus 

 shown in fig. 132. The jar A in the centre contains the 

 plant to be examined, which may preferably be represented 

 by a number of germinating peas. It is closed by a cork, 

 which is perforated in two places. Into one hole a tube is 

 inserted which passes to the bottom of the jar, and serves 

 for the admission of air. An outlet tube passes through 



FIG. 132. APPARATUS TO SHOW THE EXHALATION OF CARBON DIOXIDE BY 

 GERMINATING SEEDS. THE AIR ENTERS THROUGH THE TUBE ON THE LEFT ; 



ITS CARBON DIOXIDE IS ABSORBED BY THE POTASH IN F. IT PASSES THROUGH 

 A, IN WHICH THE SEEDS ARE PLACED, AND THE CARBON DIOXIDE GENERATED 

 THERE IS CARRIED OVER INTO C, WHERE IT IS PRECIPITATED BY THE BARYTA 

 WATER. 



the other hole from the upper part of the jar, and leads to 

 another jar, c, which is partially filled with baryta water. 

 The final outlet from c can be attached to an aspirator 

 by which a stream of air can be drawn through the 

 apparatus. Before the incoming air reaches the jar A it is 

 made to pass through another jar, F, containing a solution 

 of caustic potash which frees it from all traces of carbon 

 dioxide. To ascertain that this is secured, it passes next 

 through a jar B which contains baryta water. A stream 

 of air is then passed slowly and continuously through the 

 whole apparatus, and as it bubbles through the baryta water 

 in (Tit causes the formation of a white precipitate, which 



