WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 197 



(a) Soak some Peas in water (previously boiled) until the seed- 

 coat can be removed without damaging the embryo the coats are 

 removed to avoid introducing air with the seeds. Fill a test-tube 

 with mercury and invert it in a dish of mercury, clamping it in a 

 stand ; then pass three or four peeled Peas into the tube ; plunge 

 them with forceps under the mercury, shake them free of air, and 

 release them under the tube, when they will rise to the top. With 

 a bent tube introduce a few cubic centimetres of previously boiled 

 water into the tube to keep the Peas moist. In about three days, 

 when the gas produced has ceased to push down the mercury 

 column, introduce a little more water if necessary, then with 

 forceps slip a piece of solid potash into it ; the potash solution thus 

 formed absorbs the gas (carbon dioxide) and the mercury rises to 

 the top of the tube again. To get a more accurate quantitative 

 result, use a graduated tube, and before introducing the seeds tie 

 to each a fine wire (or sew a thread through the seed and tie it in 

 a loop) longer than the tube, so that the seeds can be withdrawn 

 before introducing the potash at the end of the experiment. Set 

 up a control with Peas killed by boiling and soaked in antiseptic. 



(b) Pass a few peeled Peas or Beans into the Torricellian vacuum 

 at the top of a tube 100 cm. long and 1 '5 cm. diameter, filled with 

 mercury and inverted in mercury ; the " vacuum " contains mercury 

 vapour but no air. To prevent the adhesion of air-bubbles to the 

 tube while filling it, pour the mercury, by a funnel with its end 

 finely drawn out in a flame, through a narrower tube extending to 

 the bottom of the tube to be filled. When the tube is inverted 

 and the seeds introduced, note (1) the temperature, (2) the baro- 

 meter reading, and (3) the length of the mercury column in the 

 tube if the tube is not graduated, gum paper strips to the tube 

 at the upper level of the mercury and at the place where the tube 

 touches the mercury in the dish. At the end of, say, 24 hours, gum 

 a strip at the upper level of the mercury, and measure the volume 

 of carbon dioxide that has been produced in an ungraduated tube, 

 this is easily done by running mercury from a burette up to the top 

 mark on the tube. From the data given in Physics text- books, 

 correct this volume for temperature, pressure, etc. 



260. Comparison of Normal and "Intramolecular" 

 (Anaerobic) Respiration. In general, the amount of carbon 

 dioxide produced in ' ' intramolecular " respiration is much less than 

 that formed in normal respiration, though in some cases e.g. 

 germinating Broad Beans the two are about equal. Alongside the 

 barometer tube used in 259 b set up a similar tube containing the 

 same number of soaked seeds, pushing the seeds up to the closed 

 end of the tube and holding them in position by pushing in either 

 a piece of coiled wire or a bored cork (in either case with an 

 attached wire long enough to withdraw the obstacle at the end of 

 the experiment). 



