AEROBIC RESPIRATION 



523 



their dry weight. Owing to its active respiration the spadix of Arum 

 italicum loses in a few hours during the period of maximum heat-produc- 

 tion one-fourth of its dry weight ', while the dry weight of a crop of fungus 

 even under most favourable conditions does not form more than one-third 

 to one-tenth of the organic food consumed, and this economic coefficient is 

 still further lessened by cultivation at a high temperature 2 . 



Methods. The apparatus in Fig. 62 is suited to demonstrate the evolution of 

 carbon dioxide from plants. The object is placed under the air-tight bell-jar g, 

 which is covered with black cloth when a green plant is used. Air is drawn 

 through the apparatus by means of an aspirator attached to <:, and before entering 

 g it passes first over pumice-stone moistened with potash in the U-tube k, and then 

 through baryta-water, which should remain clear, showing that all the carbon dioxide 

 in the air has been absorbed. After a time the taps or pinch-cocks at h and h' 

 may be opened and the current resumed, when a white precipitate of barium car- 

 bonate is formed in the vessel a containing baryta-water. In Fig. 63, the cylinder, b, 



FIG. 62. 



FIG. 63. 



contains flowers, germinating seeds, &c., and when after a time the cover is raised 

 and a lighted taper or candle introduced, the flame is extinguished owing to the 

 large amount of carbon dioxide which has accumulated. 



For quantitative determinations the following method has been frequently 

 employed. The carbon dioxide is absorbed by titrated baryta-water in Pettenkofer's 

 tubes through which a constant stream of air is drawn by means of a Stammer's 

 drop-aspirator and regulated if necessary by an Elster's gas-meter 3 . In a confined 



1 G. Kraus, tfber d. Bliithenwarme beiArum italicum, 1884, pp9, 67 (Abh. d. Naturf.-Ges. zu 

 Halle, Bd. xvi). Cf. also G. Kraus, Ann. du Jard. hot. de Buitenzorg, 1896, T. xm, p. 271. 



2 Pfeffer, Jahrb. f. wiss. Bot., 1895, Bd. XXVIII, p. 257 ; Kunstmann, Ober d. Verhaltniss 

 zwischen Pilzernte u. verbrauchter Nahrung, Leipziger Dissert., 1895; Fliigge, Mikroorganismen, 

 1896, 3. Aufl., Bd. I, p. 152. Cf. Sect. 66. 



3 For details concerning apparatus and methods, Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 

 1885, Bd. i, p. 637; Johannsen, ibid., p. 688; Elfving, Einwirkung des Lichtes auf Pilze, 1890, 



