310 MyxopliycecB 



filaments of chromatin. The investigations of Wille 1 , Zacharias 2 , 

 and Scott 3 clearly show that the cells of the blue-green Algae contain 

 a body of a nuclear character. Hegler has shown that at least in 

 some cases, the ' central body' consists of a faintly stainable ground 

 substance in which is embedded a small quantity of chromatin, but 

 that it differs from a nucleus in the absencejoLa-jmclearjnembrane 

 and nucleolus ; and the still more recent investigations of Wager 4 

 and Kohl 5 have amply confirmed these observations. Dangeard 6 

 describes a nucleus in Merismopedia, but states there is no trace of 

 a nucleolus. 



Kohl states that the nucleus of the blue-green Algge not only 

 differs from that of higher plants in the absence of a nuclear 

 membrane and nucleolus, but also in its remarkable form. It 

 possesses numerous radiating outgrowths of a pseudopodium-like 

 character, which sometimes extend as far as the cell-wall. It may 

 be that these nuclear outgrowths are in some instances partly 

 responsible for the indefinite nature of the chromatophore. In 

 addition to a certain amount of chromatic substance the nucleus 

 contains a number of granules of albuminous material, which have 

 been termed ' central granules.' These have not been observed 

 outside the nucleus. 



It would appear from these and other observations, that the 

 ' central body ' of the Myxophycese differs from a true nucleus in 

 certain essential points, such as the absence of the nuclear 

 membrane and nucleolus, and in its extraordinary form ; but at 

 the same time chromatin is undoubtedly present, and Hegler and 

 Kohl have each observed a polar separation of the chromatic 

 / substance during division, accompanied by the formation of a 

 chromatic figure. From a consideration of these facts the term 

 ' open nucleus ' suggested by Hieronymus in contradistinction to 

 the ' closed nucleus ' of higher plants, appears to be a very suitable 

 one. Hieronymus was the first to point out the presence of 

 chromatin and the absence of a nuclear membrane in the so-called 

 ' central body,' but he was of the opinion that cell-division was very 

 largely, if not quite, independent of this structure. 



1 Wille in Berichte Deutscb. Botan. Ges. 1883, p. 243. 



a Zacharias, torn. cit. 1885. 



;{ Scott in Journ. Linn. Soc. Bot. xxiv, 1887, pp. 188192. 



4 Wager in Report Brit. Assoc. 1901 (1902), p. 830. 



5 Kohl, ' Ueber die Organisation und Physiologie der Cyanophy. und die mitot. 

 Teilung ihres Kernes,' Jena (1903). 



6 Dangeard in Le Botaniste, 1892, iii. 



