Before bringing these few prefatory remarks to a close, a pleasing duty devolves upon me--that of tendering my thanks for cordial aid received from Professor Dr. EDGAR CROOKSHANK in dealing with his special subject, Bacteriology. From his valuable “Text-Book on Bacteriology” I have extracted much useful matter. I am equally indebted to Professor MARSHALL WARD, F.R.S., Cambridge, for much information on “Economic Botany,” and the great advances made in the knowledge of the uses of plants, and the industrial value of bacteria in particular. My acknowledgments are also due to the Messrs. WARNE for many illustrations placed at my disposal, and for useful facts derived from their “Royal Natural History.” It will, however, be seen that the results of a large amount of independent observation have been consigned to my pages. As the references show, recourse has been had to original sources for trustworthy, reliable information on many subjects. These are constantly, almost daily, being added to, as is made manifest by the numerous periodical publications of the day devoted to this and kindred sciences; the foremost and most important among which is that almost exclusively given to microscopical science, “The Journal of the Royal Microscopical Society of London,” the perusal of which I commend to my readers. LONDON, JULY, 1898. PREFACE TO THE FIRST EDITION. The Author of this Publication entered upon his task with some hesitation and diffidence; but the reasons which influenced him to undertake it may be briefly told, and they at once explain his motives, and plead his justification, for the work which he now ventures to submit to the indulgent consideration of his readers.