THE SEED 75 



Another test for carbonic acid is as follows. All 

 caustic alkalies readily absorb carbonic acid. I take a 

 glass tube with some carbonic acid in it, close its open 

 end with my finger, and sink it into a vessel containing 

 an alkaline solution. When I take away my finger, 

 which has been blocking the mouth of the tube, the liquid 

 rushes into it and fills it. The carbonic acid contained 

 in it has disappeared, i.e. it has been absorbed by the 

 liquid. 



With these means at our disposal for detecting the 

 presence of carbonic acid, we can now return to the 

 question : do germinating seeds breathe ? We have 

 answered already one part of the question ; we have seen 

 that germinating seeds cannot get on without oxygen, 

 and that they absorb it ; we have now to show that they 

 exhale carbonic acid, in exchange for the oxygen they 

 inhale. For the sake of clearness I will give another 

 form to the experiment. A stream of common air is 

 driven into this intermediate vessel through an aperture 

 indicated by an arrow (fig. 22 B). (How this is done 

 does not concern us here, as it is only a technical detail 

 having nothing to do with the main point of the experi- 

 ment.) The air passes in bubbles through the solution 

 of caustic alkali, depositing in it those traces of carbonic 

 acid which are always present in the air, especially in 

 a room where so many people are breathing. From this 

 vessel the stream of air, now deprived of carbonic acid, 

 divides into two parts, passes (as indicated by arrows 

 on the figure) through two vessels (c and c'), and, 

 emerging from each, bubbles through the lime water 

 in the funnels (p and h') at the top of them. The 

 vessels are identical, a stream of the same air is driven 

 into both of them ; but there is this difference, that the 

 one marked c' contains a layer of living germinating 

 hemp or bean seeds, while the other contains similar 

 seeds previously poisoned with corrosive sublimate. 

 The air in passing through the apparatus continually 



