300 Plant Physiology 



test the air in one with a lighted wax taper and in another 

 with a small dish of baryta water, comparing with similar 

 tests carried out in a bottle containing only air. Explain the 

 results and indicate the limitations of the experiment. 



Evolution of CO 2 . Pour some baryta water into a large test- 

 tube, then introduce a closely fitting perforated cork upon which 

 two or three germinating seeds may be placed ; cork and seal 

 (Fig. 69). Set up a control experiment without the seeds ; in a 

 few hours compare and discuss the results with respect to the 

 baryta water. 



Set up an apparatus as suggested in section 162 consisting of 

 a chamber with germinating seed, or other favorable material, 

 connected on the side toward the inflow of air with two wash 

 bottles of potassium hydrate, to take out the CO 2 of the air, 

 and on the side toward an aspirator or filter pump with two 

 bottles of baryta water, 1 for the demonstration of any CC>2 

 given off. Before connecting up with the baryta water bottle 

 draw air through the apparatus to remove the normal air. 

 Connect with the baryta bottle, darken the respiratory chamber 

 [Why?], and draw air through the entire series for an hour or 

 two. Describe the result. 



In quantitative work a standard method of COz determination 

 should be employed, preferably a gravimetric method, in which 

 potash bulbs are used, protected as to acquisition and loss of 

 water by calcium chlorid drying tubes. In order to demonstrate 

 anaerobic respiration in seed or other material the most satis- 

 factory simple method is to replace the air in the apparatus with 

 hydrogen. For this purpose a hydrogen generator is required 

 in connection with the other apparatus described. There is 

 evidence, however, that nitrogen is preferable to hydrogen, but 

 in most laboratories it is not practicable to employ this gas. 



Heat release during respiration. Soak for about 12 hours 



1 Make a concentrated solution of barium hydrate, with excess of the 

 barium salt, keep the bottle or flask well stoppered, and decant off or 

 pipette out the liquid, when needed, avoiding all unnecessary exposure 

 to the air. 



