GENERAL 



307 



muscle, continue its functional activity for some time after it has been 

 removed from its normal habitat. The evolution of oxygen from the 

 isolated chlorophyll body is always feeble, and soon ceases, which is hardly 

 surprising when we bear in mind the fact that the chloroplastids when 

 intact in the cell may be rendered inactive by various external agencies l . 

 The positive results quoted do not however negative the possibility that 

 the assimilatory activity of the chloroplastid is aided and sustained by the 

 relationships which exist between it and the surrounding plasma, though 

 it may be shown by means of the bacterium-method that in Spirogyra 

 oxygen is evolved only from the regions of the cell-wall upon which 

 the chlorophyll-band abuts, and hence presumably is produced only in 

 the latter 2 . 



Certain red bacteria (Monas okeni, M. vinosa ; Clathrocystis roseo- 

 persicina ; Bacterium photometricrtm), which Engelmann supposed to be 

 without chlorophyll, show a very weak evolution of oxygen when ex- 

 posed to light, but this suffices to allow these aerobic organisms to 

 grow in the absence of any external supply of free oxygen, if they are 

 illuminated 3 . 



That oxygen is evolved from the chlorophyll bodies has been proved by means 

 of the bacterium method, and hence it is generally concluded that the decomposition 

 of carbon dioxide and the production of organic substance are also localized in them. 

 It does not, however, necessarily follow that the oxygen evolved is directly derived 

 from the decomposition of carbon dioxide, for Ewart has shown that certain coloured 

 bacteria can absorb oxygen in marked amount, and evolve it again when its partial 

 pressure is reduced, in some cases in sufficient quantity to keep aerobic bacteria in 

 movement for as long as twelve hours 4 . In this case, however, the evolution of 

 oxygen is a physical phenomenon, and continues equally well in the absence of light, 

 whereas the evolution of oxygen from green organisms ceases almost immediately 

 in darkness. 



Engelmann was unable to detect any chlorophyll in the purple bacteria, but 

 Biitschli observed that Chromatium okenii, when treated with alcohol, turns green, 

 and Ewart has recently brought forward evidence to show that these purple bacteria 



phyll organs of Hydra viridis are inconclusive, for here we are probably dealing with symbiotic 

 algae. [See also Beyerinck, Bot. Zeitung, 1890, pp. 745, 784 ; Kny, Ber. d. D. Bot. Ges., Bd. XV, 1897, 

 p. 388; Ewart, Bot. Centralbl., 1897, Bd. LXVII, p. 109; Kny, ibid., LXXIII, p. 426; Ewart, I.e., 

 June, 1898, p. 33.] 



1 Ewart, Journ. of Linn. Soc., Vol. xxxi, p. 425. Klebs' (Unters. a. d. Bot. Inst. z. Tubingen, 

 1888, Bd. n, p. 555) observations upon the power of forming starch in chloroplastids contained in 

 non- nucleated masses of cytoplasm pointed in the same direction. 



2 Cf. Engelmann, Die Erscheinung der Sauerstoffausscheidung chromophyllhaltiger Zellen, 1894, 

 Figs. 7, 8, 12 (Sep.-abdr. a. d. Verh. d. Amsterd. Akad.). 



Engelmann, Bot. Zeitung, 1888, p. 663; Ewart, Journ. of Linn. Soc., Vol. XXXIII, p. 151 ; 

 Annals of Botany, Vol. xi, p. 486. 



4 Ewart, Journ. of Linn. Soc., XXXin, p. 123. 



X 2 



