It has not so far been possible to establish a _classification_ of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form. The following Bacteria are =Saprophytes=:-- _Cladothrix dichotoma_ is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, _Leptothrix ochracea_ is one of the forms of this species which, in water containing ferrous iron (_e.g._ as FeCO_{3}), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. _Leptothrix ochracea_ and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria. [Illustration: FIG. 30.--_Cladothrix dichotoma._] Those forms which, according to Zopf’s views, represent the forms of development of _Cladothrix dichotoma_ are placed together in Fig. 30. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small _Leptothrix_-like forms. _B_ shows the manner of branching and an incipient _Coccus_-formation. _C_ a _Coccus_-mass whose exit from the sheath has been observed. _D_ the same mass as _C_ after the course of a day, the Cocci having turned into _rods_. _E_ a group of Cocci in which some have developed into shorter or longer rods. _F_ one of these rods before and after treatment with picric acid, which causes the chain-like structure to become apparent. _G_ a portion of a plant with conspicuous sheath, two lateral branches are being formed. _H_ part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. _Leptothrix_-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. _K_ part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and _Leptothrix_-filaments. _L_ a portion of a branched _Cladothrix_, which divides into motile _Bacillus_-forms; the rays at the free ends indicate the currents which the cilia produce in the water. _M_ a spirally-twisted, swarming filament, before and after division into halves. _N_ part of a tree-like zooglœa with Cocci and short rods.--All of these spirilla,