256 RESPIRATION, FERMENTATION AND DIGESTION 



ble of carrying on an anaerobic respiration for extended periods, 

 in which the amount of carbon dioxide given off is nearly that 

 of the normal. The following test may be made. Soak six peas 

 for twelve hours and then remove the coats without injury to the 

 plantlets. Fill a calibrated test-tube with clean mercury, and 

 support in an inverted position in a dish of mercury. Pass the 

 peeled peas under the rim of the test-tube, using forceps to handle 

 them, and do not allow air to gain access to the tube. After 

 the peas have collected at the upper end of the tube pass in also 

 a ball of filter paper about the size of a pea saturated with water. 

 If any air has been allowed to gain entrance to the tube, it must 

 be taken down and the operations described repeated. Observe 

 1 2 and 24 hours later. Note the amount of gas collected in the 

 upper end of the tube. Its composition may be roughly demon- 

 strated if a small stick of potassium hydrate is moistened in water 

 and then passed up into the tube. If it is carbon dioxide the 

 gas will be absorbed and the mercury will rise to nearly its former 

 height. 



324. Decrease of Dry Weight by Respiration. Select 30 good 

 seeds of Zea, and determine the amount of dry matter in 10 

 of them (238). Place the remainder in a suitable germinator in a 

 dark chamber, and when the roots are a few mm. long, bring 10 

 into the light and place in a water culture apparatus (292). A 

 week later estimate the amount of dry matter in the lot growing in 

 the dark room, and in those in the light. Compare the average 

 weight per seed in the three lots. The dry weight should be 

 slightly decreased during germination, but this loss would be com- 

 pensated by the synthesis of carbohydrates in the specimens, 

 brought into the light. The etiolated plants should show a con- 

 tinued loss. It is important that the material should be handled 

 carefully and that the remains of the seed attached should be in- 

 cluded in the analyses. On this account it may be more con- 

 venient to perform the experiment with Phaseolus, and allow the 

 plants to grow ten days before taking the weights. 



325. Anaerobes. It has been shown in a previous experiment 



