In 1887 my attention was directed to a curious substance, or structure, popularly known in many parts of the country as the Ginger-beer Plant, from its association with the domestic manufacture of the well-known summer beverage so often purchased in villages and towns in various parts of the British Isles, where it is usually put up in brown stone bottles, with tied corks. My earliest specimens of the Gingerbeer plant were obtained from Mr. Thistleton Dyer, of Kew, who called my attention to its mysterious nature, and from Professor Bayley Balfour, of Edinburgh, then Professor of Botany in the University of Oxford, who exhibited specimens at a meeting of the Linnean Society in 1887. Since then I have obtained specimens from various sources in this country and abroad; and during the progress of a long series of investigations have elicitated a number of facts as to the constitution and behaviour of this remarkable agent of fermentation, which, whatever their importance, cannot fail to be of interest to all biologists. In addition to the gentlemen referred to, who kindly provided me with specimens obtained from Lincolnshire, Oxfordshire, and even from North America, I have also to thank Dr. Bansome, of Nottingham, and Mr. Adrian Brown, of Burton-on-Trent, for specimens from the towns referred to, and Messrs. Leete and Appleyard, for further supplies from Coventry and elsewhere.