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. 182. 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 
r 
Fig. 132,—APpaRaTus TO SHOW THE EXHALATION OF CarBon DroxIpE BY GER- 
MINnATING SuEDS. THE AIR ENTERS THROUGH THE TUBE ON THE LEFT; ITS 
CARBON DIOXIDE IS ABSORBED BY THE PoTasH IN F, Ir passEs THROUGH A, 
IN WHICH THE SEEDS ARE PLACED, AND THE CaRBON DIOXIDE GENERATED THERE. 
IS CARRIED OVER INTO C, WITERE IT IS PRECIPITATED BY THE BARYTA WATER. 
the other hole from the upper part of the jar, and leads to 
another jar, ¢, which is partially filled with baryta water. 
The final outlet from co 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, r, 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 
