198 WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 



If we now remove 20 c.c. of the air in the tube, the mercury will 

 rise in it to that extent. To do this, fit a flask with a rubber 

 stopper carrying a bent tube with a piece of rubber tubing on its 

 free end ; warm the flask, close the tubing with a clip, introduce it 

 into the end of the barometer tube, release the clip as the air 

 cools in the flask the latter sucks air from the tube and the mer- 

 cury rises. Compare the volumes of carbon dioxide produced in 

 the two experiments by intramolecular and by normal respiration 

 respectively. 



If experiments on intramolecular respiration are allowed to con- 

 tinue for several days, the rate at which carbon dioxide is pro- 

 duced falls off, whereas normal respiration becomes increased as 

 germination advances. Plants undergoing intramolecular respira- 

 tion grow badly, and soon pass into a pathological or unhealthy 

 condition. Moreover, this form of respiration is accompanied by 

 the production of various substances in addition to carbon dioxide, 

 and among these is alcohol, as may be proved by the following 

 experiment. 



261. Production of Alcohol by "Intramolecular" Re- 

 spiration. In order to show that alcohol is produced in the 

 higher plants by intramolecular respiration, just as is the case with 

 Yeast (411) growing in a sugar solution, and thus to demonstrate 

 the relation between intramolecular respiration and alcoholic fer- 

 mentation, we proceed as follows : Lay a quantity of Peas for a 

 minute in O'l per cent, solution of corrosive sublimate to kill any 

 Yeast-cells that may be clinging to them, rinse them with distilled 

 water that has been boiled for several minutes, and place them in 

 some of this sterilised water to soak for two days, to start germina- 

 tion. Nearly fill a large flask with the Peas, and fit it with a 

 rubber stopper through which passes a twice-bent tube with its 

 longer arm dipping into mercury. 



After the free oxygen present is used up, intramolecular respira- 

 tion begins, but if the apparatus is left for three or four weeks the 

 evolution of gas will have ceased, the seeds being now dead. On 

 turning them out of the flask, the Peas in contact with the air will 

 undergo decomposition, and if a few are sown they will fail to grow. 

 Since Pea seedlings under these conditions may produce in the 

 three or four weeks no less than 5 per cent, of their dry weight of 

 alcohol, the latter may be detected by smell, especially if the Peas 

 are rubbed up with water in a mortar. The presence of alcohol 

 may be demonstrated by adding some water to the grown-up Peas 

 and distilling off the alcohol. 



