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SOIL FLORA STUDIES.
H. JOEL CONN.
GENERAL INTRODUCTION. During the past twenty years or more, considerable attention has been given to the relation of bacteria to nitrogen-transformations in soil and in manure. This particular phase of soil microbiology has been so extensively studied because of the manifest importance of nitrogen in the nutrition of plants. There still remain, however, many other problems connected with the micro-organisms in the soil that are of fundamental importance and which must be studied before a true appreciation of the significance of soil bacteria to agriculture is possible.
There are, for example, many unanswered questions relating to the distribution, function, and associative action of the microorganisms known to be abundant in soil. These questions require a method of attack almost the opposite from that used in studying the nitrogen-transformations. The latter type of investigation starts with a known function and is directed toward the unknown organisms (or at least unknown at the outset) to which this function belongs; the other type starts with known organisms and is directed toward their unknown functions. The study of nitrogen-transformations has been centered around a few special physiological activities; while the other type of study is concerned with the general characteristics of the entire soil flora. Therefore, investigations of the latter sort may be distinguished from those of the former by calling them soil fiora studies.
In making a study of the soil flora, the first step necessary is classification. Investigations relating to the distribution or function of the micro-organisms cannot proceed far without a thoro knowledge of the kinds of organisms in question. It is not yet possible to make a complete classification of the microscopic flora of soil; but it is possible to make a preliminary grouping of the organisms. Nothing more than this is attempted in the present work; but it is hoped that this preliminary grouping may be used by later investigators and developed by them into a more extensive classification.
The results now ready for publication are to be written up in a series of five papers. The present builetin, containing the first two of these papers, is really an introduction to the three that are to follow. The three later papers are to be published in separate bulletins, and each one is to take up one of the three most important groups of soil bacteria: Actinomycetes, spore-forming bacteria, and non-spore-forming bacteria. An outline of these papers follows the "Acknowledgments."
ACKNOWLEDGMENTS. This work was begun at the suggestion of Dr. H. A. Harding (formerly Bacteriologist at this Station), whose criticisms and advice proved most valuable during the two years while the work was proceeding under his direction. During the last three years the helpful suggestions of Dr. R. S. Breed have also proved of great value. Equal acknowledgments are due to the writer's father, Dr. H. W. Conn, for the inspiration of conversation and correspondence with him in regard to the work. Lastly, credit is due to Dr. W. W. Ford, who has given much valuable assistance in determining the species of spore-forming bacteria encountered in this work.
OUTLINE OF THE SOIL FLORA STUDIES.
TECHNICAL BULLETIN No. 57.
I. The general characteristics of the microscopic fora of soil.
Limitations of the study.
Importance of these different groups.
Advantages of gelatin.
Technic at present recommended.
The classification card of the Society of American Bacteriologists.
Reasons for the inconsistent results.
TECHNICAL BULLETIN No. 58.
III. Spore-forming bacteria in soil.
B. megatherium DeBary.
B. cereus Frankland.
Gelatin colonies of the spore-forming bacteria.
TECHNICAL BULLETIN No. 59. IV. Non-spore-forming bacteria in soil.
The two principal groups.
Ps. fluorescens (Flügge) Migula.
Abundance in soil.
Fluctuations in numbers.
TECHNICAL BULLETIN No. 60.
V. Actinomycetes in soil.
The question of nomenclature.
Weakness of present methods.
The pink-spored type.