1928 Journal of Applied Microscopy 



seed-coats from three peas {Pisiim sativiati) which have been soaked from 4 to 

 6 hours, and carefully pass the peas into the tube of mercury without allowing 

 any air to enter. The peas will at once pass to the upper end of the test-tube ; 

 at the end of 86-48 hours they will have evolved a quantity of carbon dioxid 

 equivalent to their own volume. The gas may be proved to be carbon dioxid 

 by absorbing it with potassium hydroxid. With a curved pipette filled with 

 water to the extreme tip, introduce 1 or '1 c.c. of water into the test-tube, then 

 with the forceps pass in a small piece of solid potassium hydroxid which dis- 

 solves almost immediately ; shake the tube gently for a few minutes and the 

 carbon dioxid will be absorbed. 



{b^ Set up such a series of bottles as shown in Fig. 2, leaving off F and 

 attaching a hydrogen generator to A. B, D, and E contain a saturated solu- 

 tion of barium hydroxid ; A, a 20 per cent, solution of potassium hydroxid ; C, a 

 few pea or corn seedlings interspersed with pieces of damp filter paper. Allow 

 the hydrogen to flow through A, B, and C alone until all air is removed from the 

 apparatus, then connect C with D and E. After 30-45 minutes, depending on 

 the flow of hydrogen, D will contain a white precipitate of barium carbonate, 

 proving the evolution of carbon dioxid in the bottle containing the seedlings, 

 even though no oxygen be present. 



5. To Demonstrate the Evolution of Heat by Respiration. The extremely active 

 respiration of germinating seeds produces a very perceptible amount of heat, the 

 important point in conducting the experiment is to measure the heat before any 

 is lost. Proceed as follows : Place 100 c.c. of a 10 per cent, solution of potas- 

 sium hydroxid in a salt-mouth bottle of about 500 c.c. capacity, set a funnel in 

 the mouth of the bottle and put about 500 c.c. of softened peas into the funnel, 

 interspersing pieces of wet filter paper among the peas ; cover the bowl of the 

 funnel with a thick layer of cotton batting to prevent radiation of heat. Over 

 the funnel set a bell-jar with a tubulature above, and through the tubulature 

 insert a thermometer graduated to fifths of a degree Centigrade, immersing the 

 bulb of the thermometer in the peas, and filling the tubulature with cotton. 



Make an exactly similar preparation for a control, using wet sawdust in the 

 place of peas. Place the two preparations side by side in a place where they 

 will not be exposed to direct sunlight and keep the temperature as constant as 

 possible. Allow the two preparations to stand for 4 to (i hours before making 

 an observation. Final observations should be made within 24 hours, otherwise 

 the growth of bacteria in the sawdust may raise the temperature of the control. 

 The potassium hydroxid solution prevents any excess of carbon dioxid from 

 interfering with the respiration of the seedlings. 



Note. — To prepare the barium hydroxid solution used in the foregoing 

 experiments, place 50-75 g. of dry barium hydroxid in a bottle holding 2 or 3 

 liters, fill the bottle with water, and shake ; there should be enough residue to 

 keep the solution saturated. Filter off a part of the solution into another bottle 

 and keep it tightly stoppered ; use from this bottle. After using the solution it 

 may be returned to the large bottle, and used again after filtering. 

 University of Michigan. HowARD S. Reed. 



