THE IMPORTANCE OF RESPIRATION 571 



reserve store of it, as Beyerinck supposes 1 . When oxygen is admitted 

 to a culture containing reduced indigo, phosphorescence commences before 

 the latter turns blue, and this is because at first the bacteria absorb all 

 the available oxygen, either directly or from the indigo solution, before the 

 latter has time to become fully oxidized. 



Historical. After Malpighi had recognized the necessity of air for the germina- 

 tion of seeds, Senebier, de Saussure, and others proved the dependence of growth 

 upon the presence of oxygen. The lowest oxygen pressures which aerobic plants can 

 successfully withstand for prolonged periods were determined by Bert and by 

 Wieler 2 (on anaerobes, cf. Sect. 98). From the time of Dutrochet it was recognized 

 that oxygen was essential for the movements of aerobic plants, and a few contra- 

 dictory results by Kabsch were probably due to the incomplete removal of the free 

 gas. Correns' researches have established the limited anaerobic continuance of 

 certain movements, and have determined the lowest percentages of oxygen in which 

 particular movements are still possible z . After Kiihne had clearly established the 

 dependence of the protoplasmic movements of aerobes upon a supply of oxygen, 

 Clark determined the lowest limits at which streaming, ciliary, and amoeboid 

 movements were possible 4 . 



As a general rule the gradual cessation of a given activity indicates that under 

 these conditions it cannot be aroused ; indeed Bert observed that germination 

 did not occur in rarefied air in which previously active growth continues for 

 a longer or shorter time. Any diminished activity thus induced must finally act 

 injuriously, and hence plants are unable to grow luxuriantly in the presence of 

 an oxygen percentage which may at first render growth more active 5 . On the 

 optimal pressure for growth and development, cf. Sect. 100. 



1 Archiv. Neerlandaises, 1889, T. xxm, p. 420. 



2 Bert, La pression barome'trique, 1878 ; Compt. rend., 1873, T. LXXVI, pp. 443, 1276; Wieler, 

 1. c., p. 189, and there the other literature is quoted. 



3 Dutrochet, Mem. p. servir a 1'hist. d. veg. et anim., Bruxelles, 1837, pp. 186, 259; Kabsch, 

 Bot. Zeitung, 1862, p. 341 ; Correns, Flora, 1892, p. 87. 



4 Clark, 1. c., 1888, p. 273; Kiihne, Unters. liber d. Protoplasma, 1864, pp. 88, 104. 



5 Cf. Wieler, 1. c. ; Lucas, Bot. Centralbl., 1886, Bd. xxvin, p. 298 ; j accord, Rev. gen. d. Bot., 

 1893, T. v, p. 289. 



