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SCIENCE PROGRESS 



not arisen by fragmentation, but have sprung out laterally 

 from the Leptothrix thread, and assumed motility as soon as 

 they have been cast loose. There seems little doubt that these 

 motile threads developed each as a protuberance as conidia 

 do, but, instead of being cut off to form conidia, continued 

 their elongation until a certain length was reached, when 

 their liberation from the parent thread was effected by the 

 setting in of a process of constriction. 



Gallionella ferruginea (Ehrenberg) 



In nature we scarcely ever find Leptothrix without at the 

 same time meeting a peculiar organism in the shape of a long, 

 flexible, thin thread which from its earliest stages 

 shows a marked tendency to coil one end of the thread 

 round the other. Examples are shown in fig. 2 and 

 Plate II. This coiling tendency is shown in the very 

 youngest and ceases only when deposition of ferric 

 hydroxide, by stiffening the periphery, and old age by 

 the loss of capacity, make further coiling impossible. 

 The process must be regarded as a case of contact- 

 irritability, not essentially different from the irrita- 

 bility of the higher plants which enables tendrils, for 

 example, to climb round their supports. In thick- 

 ness the threads vary from \ /x to 1 J //.. Migula claims 

 to have found a delicate membrane limiting the 

 organism on the outside, but neither Adler nor the 

 Fig 2— WI *iter has been able to verify his statement. It 

 Gallionella certainly is not present in older threads impregnated 

 ferrugmea; w ith iron, when, as in the case of Leptothrix, if 

 present it would be a fairly well marked structure. 

 Multiplication takes place as in Leptothrix by fragmentation, 

 small portions of coiled threads being cast loose into the sur- 

 rounding water. These elongate and coil until the normal 

 size is attained. The writer has also observed a method of 

 conidia formation in Gallionella which is identical in all essen- 

 tials with the same process as observed in Leptothrix ochracea. 

 Sometimes the deposition of iron results in a complete oblitera- 

 tion of the form of the organism. In such cases the deposition 

 increases the breadth of the organism to two or three times 

 its normal dimensions. 



