as well as of testing the accuracy of the statements of other botanists. The results of my cultures have been from time to time published in various botanical periodicals of this and other countries, and in the Transactions of the Linnean and Royal Societies. It was at one time hoped, when the acidiospores and uredospores were shown not to be distinct species, that continued biological investigation would materially lessen the number of species of the Uredineæ. I am convinced, however, that modern botanists have erred in grouping together forms on account of the similarity of the teleutospores; for instance, the Puccinia on the Compositæ, Labiatæ, Umbelliferæ, etc. The proper limitation of species of these parasites cannot be effected on purely morphological grounds; it can only be accomplished when the morphological characters are supplemented by a knowledge of the life-history of each individual species. I am greatly indebted to my friend, Professor J. W. H. Trail, of Aberdeen, for his kind assistance in the revision of the proof-sheets. I have also to thank numerous friends and correspondents, both in this country and abroad, for information and material for experiment, amongst whom I must mention Professor Farlow, of Harvard University; Mr. W. B. Grove; Rev. Dr. Keith; Dr. P. Magnus, of Berlin; Mr. W. Phillips, F.L.S.; Mr. H. T. Soppitt; Professor P. Sorauer, of Proskau; Rev. Dr. Stevenson; Rev. J. E. Vize; the late Dr. Winter, and many others. CONTENTS. VIII. MYCELIUM OF THE USTILAGINEÆ IX. FORMATION OF THE TELEUTOSPORES OF THE USTILAGINEÆ X. GERMINATION OF THE TELEUTOSPORES OF THE USTILAGINEÆ BIOLOGY OF THE UREDINEÆ-INTRODUCTORY REMARKS. THE Uredineæ constitute a large and important group of parasitic fungi, affecting flowering plants and ferns, representatives of which are familiar to every student of nature, practical agriculturist, and working microscopist. In whatever part of the world phanerogams appear, these parasitic cryptogams accompany them. Our present object is to obtain an insight into the lifehistory and the structure of those species which are known to occur in Great Britain. Much has been elucidated concerning these points during the past twenty years, but still much remains to be discovered. They all grow as parasites upon some living plant, independently of which they cannot exist, and consist of two essential elements-spores and mycelium. The spores every one sees; the mycelium, on account of its inconspicuous nature, and because it cannot be seen without some little effort, no one takes the trouble to look B |