4 6 



INFLUENCE OF CHEMICALS 



roots into such soil. The effect is often noticeable at a distance 

 of fifteen to thirty meters from the pipes conducting the gas. 



Select four vigorous specimens 

 of tomato or geranium grow- 

 ing in pots and place them in 

 an open chamber, or out of 

 doors in a sunny situation. 

 Fasten a rubber tube to the 

 tip of a gas jet and carry the 

 other end to the pot where it 

 is attached to a metal or glass 

 tube. The metal or glass tube 

 should enter the pot by the 

 FIG. 25. Zurich germinating dish. A, drainage hole in the bottom, 



shallow dish containing water, ^earthen, Qr throug h an opening at the 

 ware vessel for seeds with perforated cove C. 



side. Fit a second pot m this 



manner, and turn on the gas at the stopcock until a faint odor of 

 gas can be detected. Note the appearance of the specimens 

 from day to day. Ten days later, disconnect the tubes and com- 

 pare the root- systems and general aspect of the treated with 

 other untreated plants. 



62. Effect of a Vacuum upon Seeds. Place a number of healthy 

 seeds of a half dozen species in a small receiver connected with an 

 air pump. Exhaust the air, and turn the stopcock. More or less 

 leakage will occur even in the best apparatus, so that it will be 

 necessary to open the stopcock daily and again exhaust the re- 

 ceiver to the full power of the pump, which should be shown by 

 a manometer gauge. After two weeks' exposure to this partial 

 pressure, remove to the air, and place in Zurich germinators. 

 Germinate a number of untreated seeds at the same time for com- 

 parison. 



The above experiment may be performed still better if the seeds 

 are placed in a glass tube with one end sealed and the other con- 

 nected with the air pump. After the air has been exhausted to 

 the full capacity of the pump, the tube is cut off and sealed at 



