102 



Elementary Plant Physiology. 



given off in respiration of germinating wheat. Sup- 

 port a small retort by means of a clamp, and stand with the 

 end of the delivery tube immersed in a dish of mercury. 

 Soak a handful of grains of wheat in water for a day, then 

 place in the bowl of the retort, and cover with a moist piece 



of filter paper. Pass a few 

 fragments of potassium hy- 

 drate through the mercury, 

 up into the tube of the re- 

 tort, and then pour enough 

 water down the tube from 

 the stoppered opening to 

 dissolve the potash. Meas- 

 ure exact level at which 

 the liquid stands on oppo- 

 site sides of the tube. 

 Close the stoppered aper- 

 ture, and seal with vaseline. 

 Set the preparation in a 

 room where it may be kept 

 at a temperature of 15 to 

 20 C. The potassium so- 

 lution should absorb all of 

 the carbon dioxide in the 

 air in the retort at the be- 

 ginning of the experiment, 

 and also all of that given 

 off by the seeds. Note the 

 level to which the liquid 

 has risen in the tube a day later, and mark exactly as before. 

 This marking should be done when the experiment stands at 

 the same temperature as at the first marking. Now dismount 

 the preparation, empty the retort, and support in an inverted 

 position at the same angle as before. Fill with water to 



r 



Fig. 76. Apparatus for estimating 

 amount of carbon dioxide given off by 

 germinating wheat. A , mercury ; B, level 

 of water ; C, seeds ; D, stopper. 



