INTRODUCTION TO IRON-BACTERIA 



157 



Fig, 96. — Lcptothrix ochracea. Showing 

 oblique ends. (See text.) 



formation of the reproductive bodies called conidia. When a thread 



is about to divide, two circular thickenings are formed, very close to 



each other (Fig. 95), and it is between these that division takes place. 



As the thickenings are often not transverse, but somewhat oblique, 



threads like the one represented 



in Fig. 96 are not uncommon. ■ 



Each of the two portions of the ===^=^===i===== 



thread elongates after separation, 



and subsequently divides in the 



same way. A conidium is formed 



in the following way : A protuberance appears on the outer part of the 



membrane ; this elongates to a certain length, and is then cut off by a 



process of constriction. A single thread may form hundreds of conidia, 



and as most of them remain attached to the thread, the latter often 



becomes invisible, being surrounded by a dense mass of these bodies 



(Fig. 97). Various stages in the development of a conidium are 



given in Fig. 98. The germination of a conidium very probably 



takes place by direct elongation. Sometimes germination takes 



KiG. 97 — Leptothrix 

 ochi-acea, covered with 

 conidia. 



Fig. 98. — Leptothrix 

 ochracea, stages in de- 

 velopment of conidium. 



Fig. 99. — Leptothrix 

 ochracea. Showing ger- 

 mination of conidia in 

 situ. 



place whilst the conidia are still attached to the parent thread, with 

 the result that the latter appears to be beset with a number of 

 quill-like structures (Fig. 99). 



Gallionella ferruginea (Ehrenberg), syn. Chlamydothrix ferruginea 

 (Migula). Though this species has been known since 1836 it is only 



