A Suggestion as to the Flagellation of the Organisms Causing Legume Nodules

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Comments on the Evolution and Classification of Bacteria

The incompleteness of our present knowledge as to the species of bacteria and their relationships makes it very easy to criticise what others have written upon their evolution and to propose modifications in the classification of the group which in their turn are open to equal criticism. There has been so much speculation along this line recently1 that a certain amount of confusion has resulted, and there is danger of increasing this confusion by discussing the subject from a new point of view. There would be little justification, indeed, for doing so, were it not for the fact that Jensen (1909) has already drawn up a detailed ancestral tree for the known groups of bacteria which has considerable merit and that the committee on classification appointed by the Society of American Bacteriologists (Winslow, et al., 1917b) has accepted many of Jensen's suggestions. This committee has given the matter so much thought and has drawn up such a well formulated report that there is danger of their recommendations being accepted in toto without sufficient scrutiny. Underlying their classification are certain assumptions as to the evolution and relationships of bacteria that should be thoroughly discussed before the report is adopted by the society. In discussing the relationships of bacteria, it is necessary to keep in mind-just as when dealing with higher forms of life-that the living species represent only the ends of evolutionary lines, and that one modern form must not be considered the ancestor of another. It is probably true that there has been a greater persistence of primitive types among bacteria than in any other group of animals or plants, because the environmen

ON THE DEVELOPMENT OF A STANDARDISED AGAR MEDIUM FOR COUNTING SOIL BACTERIA, WITH ESPECIAL REGARD TO THE REPRESSION OF SPREADING COLONIES

RESP-33