STRUCTURE AND PROPERTIES OF THE CHLOROPLASTID 313 



leucoplastids formed in darkness may become green chloroplastids when 

 exposed to light. These again may be converted into differently coloured 

 chromatophores, as for example in the ripening of a fruit ; they then lose 

 the power of assimilating carbon dioxide, although the mere presence 

 of another pigment does not render the latter process impossible as long as 

 any chlorophyll is retained l . Indeed, among Algae the association of the 

 chlorophyll with a brown or red pigment is a normal phenomenon. Thus 

 it is permissible to term all chromoplastids which contain chlorophyll, 

 chloroplastids, on account of their special functional importance, and in case 

 of need the terms rhodoplastid, phaeoplastid, &c. can also be used. 



The shape of a chloroplastid may be markedly affected by the nature 

 of the cell in which it lies 2 , but the Conjugatae render evident the fact 

 that specific differences may also exist between different chlorophyll 

 bodies. The external resemblance between the chloroplastids of all higher 

 plants does not necessarily indicate that they are completely identical, 

 and it is quite possible that the chloroplastid of a pine tree could not 

 possibly exist in the protoplasm of an oak, for chloroplastids are dependent 

 for their growth and maintenance upon the existence of certain specific 

 relationships with the surrounding plasma, just as is the case also with 

 the nucleus and all plasmatic organs 3 . This also applies to those Algae 

 which live symbiotically in the bodies of certain animals, and which from 

 a physiological standpoint bear a similar relationship to the animal cell 

 which contains them, as do chloroplastids to their parent cell (Sect. 65). 



The presence of chromatophores does not necessitate a formation of 

 chloroplastids, for in non-chlorophyllous phanerogams the former may occur 

 but not the latter, and in Fungi all organs of the nature of either chloro- 

 plasts or chromoplasts seem to be absent. Chlorophyll is apparently never 

 uniformly distributed throughout the cytoplasm even in the lowest unicellular 

 organisms 4 . Chromatophores may serve a variety of purposes, and it is of 

 great importance to notice that chromatophores which are unable to turn 



Zimmermann in Beibl. z. Bot. Centralbl., 1894, Bd. IV, p. 90; Schimper, Jahrb. f. wiss. Bot., 1885, 

 Bd. xvi, p. i. Ewart (Joum. of Linn. Soc., xxxi, 1896, pp. 390, 427, 438, 449-452, 569, 573~57 6 ) 

 has shown that in adult cells no reformation of the chloroplastids is possible when these have been 

 killed, but it is possible that in embryonic cells masses of plasma may directly differentiate into 

 chloroplastids, as for example when a root meristem becomes converted into a green shoot. 



1 Ewart, I.e., pp. 390, 437, 448, 451. 



On the occurrence of differently shaped chloroplastids in the same plant, see Zimmermann, 

 Pflanzenzelle, 1887, p. 48; Haberlandt, Flora, 1888, p. 291. 



3 Cf. Sects. 4, 7, 8, and Pfeffer, Aufnahme u. Ausgabe ungeloster Kb'rper, 1890, p. 174; Cela- 

 kovsky, Flora, 1892, Erganzungsband, p. 224. 



4 On Cyanophyceae, &c., cf. Zimmermann, 1894, I.e., p. 97. On the supposed peripheral 

 distribution of the Bacterio-purpurin in red Bacteria, see Sect. 52 ; A. Fischer, Unters. ii. Cyanoph. 

 u. Bact, 1897, pp. 25, 119. Diffuse masses of cytoplasm tinged with chlorophyll may also occur 

 normally in the cells of certain phanerogams, without the power of carbon dioxide assimilation being 

 lost. See Ewart, I.e., pp. 449, 569; Wiesner, Pringsh. Jahrb., Bd. vm, 1872, p. 575. 



