CYANOPHYCE& 449 



the filiform condition. This cylindrical condition, when attained, is 

 usually unstable, but becomes stable in Synechococcus. Glceocapsa may 

 also pass into an encysted filiform condition in Sirosiphon (see p. 439). 

 Zopf insists on the close affinity between the blue-green Schizo- 

 phycese and the Schizomycetes. Hansgirg regards many of the forms 

 included under Chroococcus as resulting from the breaking up of fila- 

 ments of the higher Cyanophyceae such as Lyngbya, while Glceocapsa 

 may be derived in the same way from Stigonema, and Synechococcus from* 

 Calothrix. He believes, in fact, most if not all of the organisms hitherto 

 included in this family to be connected, by retrogressive metamorphosis, 

 with other more highly developed forms, and even possibly in some 

 cases (Flora, 1886, p. 291) with the protoneme of a moss. Microcystis 

 is regarded by Richter (Hedwigia, 1885, p. 18) as a resting-form of 

 Euglena. The Chroococcaceae, like the other Cyanophyceae and the 

 Protococcaceae, enter largely into the composition of Lichens. The 

 reader will find this subject amply treated by Bornet in his ' Recherches 

 sur les gonidies des Lichens ' (Ann. Sci. Nat., 5 Ser., xvii. and xix.). 



LITERATURE. 



Nageli- Gattungen einzelliger Algen, 1849. 



Borzl Nuov. Giorn. Bot. Ital., 1878, p. 369 ; and 1879, p. 47. 



Richter Hedwigia, 1880, pp. 154, 169, 191. 



Zopf Bot. CentralbL, x., 1882, p. 32; and Ber. Deutsch. Bot. Gesell., 1883, 



P- 319' 



Tangl Anzeiger Akad. Wiss. Wien, 1883, p. 87. 

 Hansgirg Oesterr. Bot. Zeitschr., 1884, pp. 313, 351, 389; and Bot. Centralbl. 



xxii. and xxiii., 1885. 



GROUP II. AND CLASS XXVIIL SCHIZOMYCfTES 

 (BACTERIA). 



Though this group has been the subject of a great deal of investiga- 

 tion and much speculation, it cannot be said that our knowledge of it 

 is in due proportion to the literature. The minute size of the cells pre- 

 cludes an exact study of their structure. This leads to errors of deter- 

 mination and to confusion of forms in culture experiments, and thus 

 renders difficult the study of the course of development. A large number 

 of the investigators have been and are unequipped with a knowledge 

 of natural history, and are unfitted to appreciate the significance of 

 phenomena observed, or, in other cases, are incapable of observation of 



G G 



