GENERAL 



305 



possible by various agencies to inhibit the power of carbon dioxide assimila- 

 tion for a longer or shorter time without perceptibly affecting the shape 

 or colour of the chloroplastids (Sect. 58). Hence it is evident that the mere 

 presence of chlorophyll in the cytoplasm will not necessarily confer a power 

 of assimilating carbon dioxide upon it, for the process can only proceed when 

 the proper functional relationship exists between the two *. Hence it is not 

 impossible that normal green chloroplastids may be found which never 

 develop any power of assimilating carbon dioxide, and in all cases the 

 assimilatory activity of a chloroplastid is not dependent solely upon the 

 amount of chlorophyll which it contains. 



The chloroplastids are often coloured red or brown by an admixture 

 with other pigments, but the latter do not hinder the process of carbon 

 dioxide assimilation, and may indeed be of importance in rendering certain 

 rays of light available for use (Sect. 60), although when combined with the 

 plasma of a non-chlorophyllous chromatophore they confer upon it no 

 power of photosynthetic assimilation. Thus red and yellow chromatophores 

 in which no chlorophyll is present, as well as colourless leucoplastids, cannot 

 assimilate carbon dioxide, and the purple bacteria are able to assimilate 

 apparently only because they contain a certain amount of chlorophyll, for 

 other coloured bacteria in which no chlorophyll is present have not this 

 power 2 . It is, however, not impossible that colourless organisms may 

 exist which are capable of assimilating carbon dioxide when exposed to 

 light or to heat rays ; indeed we are acquainted with certain colourless 

 bacteria which are actually able to assimilate carbon dioxide by means of 

 chemical energy (Sects. 50 and 63). 



No living chlorophyllous chromatophore has as yet been observed which per- 

 manently exhibits an entire incapacity for photosynthetic assimilation, and Ewart 

 has shown that an inherent power of carbon dioxide assimilation resides in all the 

 chloroplastids which Dehnecke supposed were permanently inactive. Thus the 

 green starch-bearing plastids in the stem of Pellionia and other plants are able to 

 assimilate carbon dioxide when the starch is partially or entirely removed 3 . Similarly 

 the chloroplastids of Euphrasia offidnalis exhibit an active power of carbon 

 dioxide assimilation, but are readily rendered inactive by injurious external agencies 

 (Sect. 58). It was apparently owing to a condition of temporary inactivity having 



(ibid., 1886, T. en, p. 264), Pringsheim (Ber. d. Bot. Ges., 1886, p. Ixxxvi), and Beyerinck (Bot. 

 Zeitung, 1890, p. 742). 



1 [The cells of certain phanerogams may contain diffuse chlorophyll, and yet be able to assimilate 

 (Ewart, Journal Linn. Soc., Vol. xxxi, pp. 449, 569). We are probably dealing here with nn- 

 differentiated chlorophyll corpuscles.] 



2 Ewart, Annals of Botany, xi, 1897, p. 486; Journal Linn. Soc., Vol. xxxm, 1897, 

 pp. 123, 147. 



3 Dehnecke, tJber nicht assimilirende Chlorophyllkorper, Bonn, 1880, p. 45 ; Ewart, Assim. 

 Inhib., Journ. of Linn. Soc., 1896, xxxi, p. 436. 



PFEFFER X 



