CH. I] RESPIRATION. 11 



(7) Another method. 



The Torricellian vacuum was used by Wortmann in 

 his work on intramolecular respiration 1 . A tube closed 

 at one end, and of greater length than the height of the 

 barometric column, is filled with, and inverted over 

 mercury. Three or four peas are floated into the vacuum 

 at the top of the tube. After 24 hours a depression of 

 several cm. will be observed in the height of the column, 

 which will, on the addition of KHO, rise to about its 

 original level, allowance being made for any change in 

 the barometer. 



(8) Pfeffers method. 



To get accurate results another method must be 

 followed ; the following is taken from Pfeffer's paper in 

 his Tubingen Untersuchungen, Vol. I. p. 637. 



The principle is that described in Exp. 3 for estimating 

 ordinary respiration, but instead of air, a current of 

 hydrogen is drawn through the vessel in which the plants 

 are contained. It is necessary to prevent the entrance 

 of extraneous C0 2 and to make sure that the hydrogen 

 has no admixture of oxygen. 



(9) Rise of temperature' 2 . 



The following is Sachs' arrangement for showing the 

 rise of temperature in germinating peas 3 . We have found 

 flowers, such as those of the dandelion (Taraxacum), 



1 Sachs' Arbeiten, n. p. 500. 



2 The spadix of Arum is the classical material for demonstrating the 

 heat produced by the respiration of plants. The rise of temperature only 

 occurs during such a limited time that the experiment constantly fails 

 and is not to be recommended for class-work. 



3 Sachs' Text-book, Ed. n. p. 724. Fig. 472. 



