838 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
membrane. Instead of a complicated interwoven network, there is in 
it always a single nuclear filament only. Whether this central body 
is called a nucleus or not is a matter of comparative indifference ; the 
author proposes to designate it an “ open ” nucleus, in contradistinction to 
the “ closed ” nucleus of higher organizations. Cell-division appears to 
be entirely independent of the condition of this central body. 
Crystals of cynanophycin were found in several instances in the 
nuclear filament. The author gives, in great detail, the microchemical 
reactions of cyanophycin, and concludes that, although not identical with 
nuclein, chromatin, or pyrenin, it is a substance of the same nature, and 
that it corresponds to the granular constituents of the nucleus of higher 
plants. It also apparently serves as a reservoir for nitrogen ; and this 
is no doubt connected with the symbiotic association of species of Nostoc 
and Anabaena with such plants as Blasia , Anthoceros , Azolla, Cycas , and 
Gunnera. 
Herr E. Zacharias * criticizes on various points both these observa- 
tions and those of Zukal.f He denies the accuracy of the term 
“ nucleus ” as applied to the central body of the Cyanophycese, and 
maintains that we have no knowledge of the part which it plays in the 
economy of the cell. 
Coccoid Condition of a Nostoc.f — M. C. Sauvageau describes a 
hitherto unknown mode of propagation in a Nostoc , probably N. puncti- 
forme. The propagating cells resemble the spores or cysts, but con- 
tinue to divide until they form amorphous colonies similar to those of 
ApJianocapsa and other Chroococcaceas. The same individual may be 
made to pass alternately from the ordinary Nostoc to the coccoid con- 
dition, and vice versa ; this is the first example of such pleomorphism 
known among heterocystous algee. In the coccoid condition the cells 
are of a grey-brown colour ; when about to pass into the Nostoc condi- 
tion, a cell separates from the rest, developes the blue-green pigment, 
and forms a filament by repeated divisions. 
M. P. Hariot § identifies the so-called Anabaena found in the cells of 
Cycas, and the Nostoc in those of Gunnera , as chroococcoid forms of 
Nostoc punctiforme , of which N. Hederulae and Polycoccus punctiformis 
are synonyms. 
0scillariace3e.|| — M. M. Gomont publishes a Monograph of the 
Oscillariacese or Homocystous Nostocaceee. The order is divided into 
two tribes — the Vaginarieae, in which a number of trichomes are enclosed 
within a common sheath, and the Lyngbyeae, in which, when a sheath 
exists, it encloses only a single trichome. 
The Oscillariaceae are distinguished by not having cells differentiated 
either into heterocysts or hairs, and by having no true branching. 
True spores have been found only in a single species. The cell is 
enclosed in a distinct membrane, which is never wanting, even in the 
hormogones. It does not exhibit the reactions of cellulose, but rather 
those of fungin or cutin. Notwithstanding its tenuity, it is composed of 
distinct layers. The protoplasm of the cell is granular, and contains 
* Bot. Ztg., 1. (1892) pp. 617-24. f Cf. this Journal, ante, p. 655. 
% Comptes Rendus, cxv. (1892) pp. 322-5. § Tom. cit., p. 325. 
H Ann. Sci. Nat. (Bot.), xv. (1892) pp. 263-368 (9 pis.). 
