viii.] Aquatic Saprophytes. Cladothrix. 77 



laterally out of the line of the rest, and then growing on in the di- 

 vergent direction and dividing transversely. 

 The divergent branch forms an acute angle 

 with the primary filament, and in relation 

 to the point of attachment or base of the 

 latter the angle is usually open upwards, 

 seldom the reverse. This form of branch- 

 ing, which is of common occurrence in the 

 Nostocaceae, in Scytonema, for example, 

 and Calothrix, has been termed false 

 branching, because the part which the 

 individual cells take in it, morphologically 

 speaking, is not the same as in most 

 of the other lower plants which have 

 filaments formed of a single row of cells ; 

 it is false only in this sense, and is really 

 a peculiar mode of branching. 



Whatever else is known of the structure 

 and development of Cladothrix, especially 

 since Zopfs researches, so far agrees 

 with the accounts given of Crenothrix, 

 that only a few remarkable particulars 

 need be touched upon here; Zopfs 

 monograph should be consulted. First 

 of all it is not perhaps superfluous to re- 

 mark that Cladothrix also receives a de- 



Fig. 6. 



posit of iron oxide in the sheaths of its filaments, and becomes 



Fig. 6. Cladothrix dichotoma, Cohn. a extremity of a live filament, which 

 grew originally in the direction r p. The branches n, n have been formed 

 by lateral divergence and subsequent growth of segment-cells in the new 

 direction. The construction of the filament out of cylindrical segment-cells 

 is clearly shown at the apex of the branches ; elsewhere it is recognisable 

 only by the aid of reagents, b portion of a filament showing the segmen- 

 tation and the sheath ; the latter is empty in its upper half, except 

 where one cylindrical cell remains fixed in it. Magn. 600 times, but made 

 a little too broad in the drawing. 



