Myxophycece 309 



The pigment in the cells of the Myxophycese is unquestionably 

 variable in its disposition, and although in certain of these plants it 

 occupies a somewhat indefinite extent of the cytoplasm, in others 

 it is undoubtedly collected into definite areas. It must be re- 

 membered, however, that indefiniteness of the pigmented areas is 

 not confined to the blue-green Algae alone, but is often observed 

 in some of the lowly Protococcoidese, and even in such a highly 

 specialized group as the Desmidiacese. 



Kohl has regarded each of these minute granules of pigment 

 as a chromatophore, but I prefer to adopt Hegler's idea of a 

 cyanoplast for that part of the protoplasm in which the granules 

 of pigment are collected. This cyanoplast, which can be regarded 

 as an archaic type of chromatophore, exhibits much variation in 

 the degree of its differentiation, and attains in one family the 

 Glaucocystacea? the highly differentiated condition met with in 

 the higher groups of Algae. This is one of the reasons which 

 has induced me to primarily subdivide the Myxophycese into the 

 Glaucocystidese and the Archiplastidese. 



The pigment is generally confined, as mentioned above, to the 

 more peripheral areas of the protoplasm, the clear central portion 

 of which often stands out prominently as a rounded mass. This 

 has received the name of the 'central body' and of late much 

 attention has been given it, more particularly with the view of 

 determining whether it should be regarded as a nucleus or not. 

 Most _ of the recent _ Jnvestigations show that JJiaJj2iiO-tral -body ' 

 differs considerably in its structure from the cell-nucleus of higher 

 plants. 



Stockmeyer and Zukal have each denied that the 'central body' 

 has any relation to the nucleus of higher plants, and Marx 1 stated 

 that he had obtained negative results in his search for a nucleus. 

 Zacharias 2 states that the term ' nucleus ' should not be used for 

 the ' central body ' as nothing is known of the part it plays in the 

 economy of the cell, and Massart affirmed that there was no reason 

 to consider it as a nucleus as it was sometimes vacuolated and had 

 no definite outline. Fischer, and also Palla 3 , found no chromatin 

 in the ' central body ' of the blue-green Alga? they examined, but 

 other observers have described the presence of both granules and 



1 Marx ' Untersucb. liber d. Zellen d. Oscillarien,' Erlaugen, 1892 (vide Bot. 

 Centralbl. liii, 1893). 



2 Zacharias in Bot. Zeitung, 1892, 1. 



a Palla in Pringsheim's Jahrb. fur wissensch. Bot. 1893, xxv. 



