no 



GROWTH AND WORK OF PLANTS 





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. 88, with the small 



ends, one in a vessel containing a 

 strong solution of barium hydrate, 

 and the other in a vessel contain- 

 ing a strong solution of caustic 

 potash (one stick of caustic potash 

 in two-thirds tumbler of water). 

 Red ink, or some red analine 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 

 consistency. If the experiment is 

 properly set up, in twelve to twenty- 

 four hours the liquid will be seen 

 to be rising in the tubes. 



184. Why the liquid rises in 

 the tubes. From the experiment 

 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. 88. 



Apparatus to show respiration of ger- 

 minating wheat. 



