THE INFLUENCE OF THE EXTERNAL CONDITIONS 565 



of conserves to explode probably possess a similar power. Sabrazes and 

 Bazin 1 observed that certain bacteria remained living for days in carbon 

 dioxide at a pressure of fifty atmospheres, whereas in other cases d'Arsonval 

 found that death ensued under these circumstances. The action of the 

 increased pressure of carbon dioxide is apparently a physiological one, for 

 a very much higher pressure would be necessary to direct'y prevent the 

 liberation of this gas. (For the inhibiting action of other fermentative 

 products, cf. Sects. 86, 92, 103.) 



Percentage of water z . Thoroughly dried seeds 3 , mosses and lichens 

 do not respire, although respiration commences when but little water is 

 present and rapidly increases as more is absorbed. On the other hand, 

 the injection of the stomata or intercellular spaces with water renders 

 gaseous interchanges more difficult and thus diminishes the respiratory 

 activity. Hence Kreusler found that leaves respire most actively when in 

 the normal turgid condition. Aubert found this to be the case in plants of 

 the Crassulaceae and Jumelle in lichens. 



Injuries and wounds. Owing to the plant's reactive power, a wound 

 becomes covered by callus or wound- cork, and at the same time more 

 or less markedly increased respiratory activity is usually excited. This 

 was first shown by certain isolated observations made by Bohm and by 

 Stich, while Richards has recently studied the phenomenon more in detail 

 and has established its general importance 4 . 



Tubers and other resting organs react most markedly : thus 300 grms. of small 

 potatoes evolved at the laboratory-temperature 1-2 to 2 mgrm. CO 2 per hour, but 

 after being cut into four pieces 9 mgrm. were evolved during the 2nd hour, 14-4 

 during the 5th, 16-8 during the gth, 18-6 during the 28th, 13-6 during the 5ist, 3-2 

 per hour after four days, and 1-6 mg. per hour after six days. In other cases also 

 the reaction is a transitory one, the maximum being attained in leaves usually in 

 a few hours, and these commonly do not even attain a doubled production of 

 carbon dioxide in spite of numerous incisions having been made. 



two atmospheres, owing to the carbon dioxide evolved by intramolecular-respiration, but it is 

 possible that micro-organisms may have aided in producing this result. 



1 Sabrazes u. Bazin, Koch's Jahresb., 1893, p. 34; d'Arsonval, Compt. rend., 1891, T. cxn, 

 p. 667. 



2 Seeds: Detmer, Landw. Jahrb., 1882, Bd. xr, p. 229; Kreusler, ibid., 1885, Bd. xv, p. 951 ; 

 1887, Bd. xvi, p. 748. Mosses and lichens: Bastit, Rev. gen. d. Bot, 1891, T. in, p. 476; Aubert, 

 ibid., 1892, T. iv, p. 379; Jumelle, ibid., 1892, T. iv, p. 169 ; Lund, ibid., 1894, T. vi, p. 353; 

 Jonsson, Compt. rend., 1894, T. cix, p. 441. 



3 [Living seeds always retain a trace of imbibed water, even when dried in a desiccator, and this 

 may amount to as much as i or 2 per cent., or in the case of certain lichens the minimal water 

 percentage consistent with the preservation of vitality may be more than 5 per cent. Cf. Ewart, 

 Trans. Liverpool Biol. Soc., 1897, XI, p. 151 ; Schroder, Unters. a. d. Bot. Inst. z. Tiibingen, 1886, 

 Bd. II, Heft i, p. 5.] 



4 Bohm, Bot. Zeitung, 1887, p. 686; Stich, Flora, 1891, p. 15; Richards, Annals of Botany, 

 1896, Vol. x, p. 531. (Abstract by Pfeffer in Ber. d. Sachs. Ges. d. Wiss., 1896, p. 384.) 



