I04 SULPHUR BACTERIA 



magnification the thread appears to be segmented, but with 

 a higher magnification no signs of segmentation are seen. 

 The disposition of the plasma is seen in Fig. 8A. Small pro- 

 jections of plasmatic material appear to jut out from the sides. 

 The projections take the form of very irregular-shaped rods 

 and point in all directions. There thus appears to be a single 

 continuous vacuole along the whole length of the thread, 

 occupying the space not filled up with the plasma. It is 

 possible that transverse walls may be a feature in the further 

 development of the threads, but such w^ere not observed. 

 Opportunities for studying the life-history of this organism 

 have not yet occurred, but it is unlikely that it is identical 

 with the Beggiatoa mirabilis of Cohn and of Hinze. 



In Hinze's account of Beggiatoa mirabilis the appearance 

 and development of the transverse walls are given. Its 

 development begins with the formation of a ring-shaped 

 flat projection round the inside of the cell (Fig. 8^). This is 

 shown diagrammatically in Fig. 8/. This annular plate is 

 pushed during development farther and farther inwards until 

 the growing wall stretches across the whole cell. By inter- 

 calary growth the dividing cells attain the size of the mature 

 cells. According to Hinze some of the cells die oft and sepa- 

 ration takes place at these points. Each of the separated 

 threads then elongates afresh. They are naturally straight 

 and of a somewhat stift' consistency, but become somewhat 

 wavy from the unequal distribution of the numerous particles 

 of dirt and other debris w^hich settle on their surface. 



Beggiatoa arachnoidea (Agardh), Rabenhorst (2), 1865. 



Literature. — Agardh (2), 1827; Corda (l), 1835, (2), 1836; 

 Kutzing (2), 1843 ; Cohn (5), 1865 ; Warming, 

 1875 and 1876; Engler, 1883; Koppe, 1923; 

 Bavendamm, 1924. 



Description. — This organism was first mentioned by Agardh 

 under the name Oscillatoria arachnoidea. Since that time 

 several changes in nomenclature have occurred, and in 1865 

 Cohn transferred it to the genus in which it is now placed. 



