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. 182. The jar ain 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 
Fic. 182.—ApPpaRaTUS TO SHOW THE EXHALATION OF CarsBon DiI0xIDE BY 
GERMINATING Sprps, THE AIR ENTERS THROUGH THE TUBE ON THE LEFT; 
ITS CARBON DIOXIDE IS ABSORBED BY THE POTASH IN F, Iv 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, 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 c it causes the formation of a white precipitate, which 
