294 



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 GER- 

 MINATING 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 DlOXIDE 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 o it causes 

 the formation of a white precipitate, which analysis shows 



