n8 



GROWTH AND WORK OF PLANTS 



T 



begun to sprout the bulbs of two thistle tubes are filled with the 

 sprouted grains. A piece of sphagnum moss, or loose cotton, 

 can be placed in the lower part of the bulb to prevent the grains 

 from falling down the tube. The tubes may be supported as 

 shown in fig. 91, with the small ends, one in a vessel containing a 



strong solution of barium hydrate, 



and the other in a vessel containing 

 a strong solution of caustic potash 

 (one stick of caustic potash in two- 

 thirds tumbler of water). Red 

 ink, or some red aniline dye, may 

 be added to the solution to make 

 the liquid visible as it rises in the 

 tube. Each bulb is closed airtight 

 by a piece of glass cemented down 

 with vaseline of sufficient consis- 

 tency. If the experiment is pro- 

 perly set up, in twelve to twenty- 

 Mi I .Jj~~~~~ r four hours the liquid will be seen 

 Ifey to be rising in the tubes. 



188. Why the liquid rises 

 in the tubes. From the experi- 

 ment with the germinating peas 

 we know that barium hydrate 

 absorbs carbon dioxide. The potash solution also absorbs 

 carbon dioxide. The germinating wheat during respiration, i.e., 

 while it breathes, gives off carbon dioxide just as the peas do. 

 The carbon dioxide being heavier than the air settles down in 

 the tube and comes in contact with the potash solution and is 

 absorbed. Now at the beginning of the experiment the thistle 

 tube, and the space between the wheat grains, was filled with air. 

 If no portion of the air was taken from the tube the liquid could 

 not rise as the carbon dioxide is absorbed. This experiment 

 proves then that some constituent of the air is absorbed by the 

 germinating wheat grains and undergoes a chemical change in 

 the wheat seedlings. 



Fig. 91. 



Apparatus to show respiration of 

 germinating wheat. 



