36 



EXPERIMENTS WITH PLANTS 



soaked seeds, the other with moist cotton (to make the 

 conditions equal so far as evaporation is concerned), 

 and a piece of cardboard is laid over the top. The 

 thermometers are inserted to equal depths and read- 

 ings are taken every fifteen minutes. A difference of 

 more than a degree is not to be expected in most 

 cases and it is often less than this. The tumblers 

 must not be placed in the sunlight. 



How do seeds get air under ground? Does the soil 

 contain air? Fill a bottle just half-way to the neck 

 with the soil to be tested; place a thin layer of wet 



32, Method of measur- 

 ing the temperature 

 of germinating seeds 

 (control at right). 



