THE IRON-BACTERIA 375 



which gradually grows into a thicker and stiffer membrane as 

 it becomes impregnated with ferric hydroxide. When the 

 protoplasm dies the sheath sinks to the bottom and contributes 

 its mite to the general stock. 



To observe Leptotkrix ochracea in the living condition the 

 ochre-waters are kept under observation, particularly at the 

 close of winter and during the autumn months. There will then 

 be found fluffy brown-red streamers waving in the water, and 

 attached to bits of grass or to stones under the water. These 

 will probably be living threads of Leptotkrix ochracea, and we 

 will describe it first. 



Leptotkrix ochracea (syn. Chlamydothrix ochracea) (Kiitzing) 



The cylindrical, unicellular threads of Leptothrix are (^ 

 easily recognisable. The ends are rounded and the 

 membrane, or sheath, is a delicate covering which a 

 judicious staining renders visible. The threads measure 

 from i ytt x to 2 /j, in breadth according to the age and 

 to the amount of deposition which has taken place 

 (fig. i ). Old threads may show a measurement of 3 /j, or 

 about double the average width. This happens when 

 the deposition of ferric hydroxide has been very active. 

 Reproduction takes place by fragmentation, small or 

 large portions being liberated by a process of constric- 

 tion. The liberated portions grow in length and repeat 

 the process. When this takes place the length of the 

 thread is not very great, but when the period of 

 fragmentation comes to an end the threads elongate and 

 may then reach a length of 200 /u, or more. Another 

 method of reproduction is by the formation of conidia. 

 A little swelling is formed on the outer surface, and 

 when this reaches a certain size a process of constriction 

 takes place resulting ultimately in the liberation of a 

 small oval cell, the conidium. These conidia are formed 

 over the whole surface. Germination takes place, 

 probably by direct elongation, and a new thread is figTT- 

 formed. Pure cultures have been obtained in artificial Leptotkrix 

 media by Molisch. In such cultures conidia formation ochracea '> 

 does not take place, but there is instead a liberation of 

 " Schwarmer." These are short threads which have evidently 



1 1 /x. = 1/1000 mm. 



