36 ] The Classification of Lower Organisms 



In Scytonema, the pressure of multiplying cells causes waves of the filament to break 

 laterally through the sheath and produce branches in pairs. Plectonema branches 

 like Tolypothrix but has no heterocysts. 



Family 6. Chlamydotrichacea [Chlamydotrichaceae] Pribram in Jour. Bact. 18: 

 377 (1929). Aquatic organisms consisting of colorless cylindrical cells in sheathed 

 filaments, without heterocysts but exhibiting false branching, the sheaths of young 

 filaments thin and colorless, those of older ones thick and yellow to brown. Chlamydo- 

 thrix ochracea Migula was intended as a new name for Leptothrix ochracea Kiitzing, 

 but the entity to which it is believed to apply is totally different from the one to which 

 the latter name was applied above. Chlamydothrix is a filament of definite cells 

 about 1 ^ in diameter. The only other definitely characterized species of this family is 

 Clonothrix fusca Roze, the cells about 2^ in diameter, those near the tips of the fila- 

 ments dividing repeatedly (always in one plane) to produce spherical non-motile 

 gonidia (Kolk, 1.938). 



Family 7. Fdvulariacea [Rivulariaceae] Rabenhorst op. cit. 101. The filaments 

 include heterocysts and exhibit the false branching of Tolypothrix; the outgrowth 

 of the filament below each heterocyst gives to the original terminal part the appear- 

 ance of a branch of which the heterocyst is the basal cell. The ends of the filaments 

 become attenuate and colorless. In Calothrix the filaments are mostly solitary; in 

 other genera they remain together in gelatinous colonies. Rivularia is without spores; 

 in Glocotrichia there is a large cylindrical spore next to each heterocyst. 



Family 8. Sirosiphonacea [Sirosiphonaceae] Rabenhorst op. cit. 114. Family 

 Stigonemataceae Kirchner 1898. This family takes its name from the ancient generic 

 name Sirosiphon Kiitzing 1843, which turned out to be identical with Stigonema 

 Agardh 1824. The cells divide at first in one plane and produce filaments. Presently 

 they exhibit a capacity to divide in other planes, and may produce true branches or 

 multiseriate filaments or both. Heterocysts and spc^es are generally produced. 



Family 9. Pleurocapsacea [Pleurocapsaceae] Geitler in Pascher et al. Siisswasser- 

 Fl. Deutschland 12: 124 (1925). This group was formerly included in Chamaesi- 

 phonacea, but it appears probable that Chamae siphon is related to Oscillatoria, and 

 the present group to Stigonema. Most of the Pleurocapsacea are marine, epiphytic 

 on seaweeds. Their apparently typical behavior, as exemplified by Hyella and 

 Radaisia, consists of the production of branching filaments whose terminal eel's be- 

 come enlarged, after which their contents undergo division in many planes to produce 

 numerous minute spores called gonidia. In Pleurocapsa and Xenococcus there is no 

 filamentous phase; the gonidium gives rise to a cluster of cells all of which produce 

 gonidia. In Dermocarpa the gonidium gives rise to a single vegetative cell which 

 divides only to produce gonidia. 



Family 10. Crenotrichacea [Crenotrichaceae] Hansgirg. This family includes the 

 single known species Crenothrix polyspora Cohn, one of the traditional iron bacteria. 

 There is every appearance that it is a colorless variant of the Pleurocapsacea. A germi- 

 nating gonidium gives rise to an unbranched filament of cells, about 2^ in diameter, 

 in a sheath which is at first thin and colorless, later becoming thicker and discolored 

 by ferric oxide. Some cells may burst from the free end of the sheath as macrogonidia. 

 Others may begin to divide lengthwise. These may at first grow before re-dividing, 

 and may swell the sheath to a fusiform or trumpet-like shape. By further division 

 they produce numerous microgonidia, which may sift out of the sheath or be re- 

 leased by its decay. 



Such are the Mychota, the organisms which may properly be characterized as 

 lacking nuclei. 



