14 INTRODUCTION 



life history of the Mycetezoa (1859). He maintained his interest in this 

 group of organisms for many years and inspired the work of many 

 outstanding students in this field. Probably the most outstanding of 

 de Bary's earlier studies was that in which he determined the life cycle 

 of the rusts (Uredinales) and proved the heteroecious nature of black 

 stem rust of small grains {Puccinia graminis Pers.). In the two decades 

 after the appearance of this work (1865) we find many of de Bary's pupils 

 following and extending life history studies in all groups of fungi. Pre- 

 eminent among these was Oscar Brefeld, who employed, not for the first 

 time but probably most extensively up to then, the method of growing 

 the fungi under study in pure culture on various types of culture media 

 and under various external conditions. In this way he was enabled to 

 study the developmental stages of many fungi and to learn much of their 

 physiology as well. His chief series of contributions began in 1872 and 

 the last volume appeared in 1912. One of de Bary's early students and 

 collaborators was the Russian, M. S. Woronin (1838-1903), who returned 

 to Russia after several years of association with his great teacher, there 

 becoming in his turn the center of a group of very able mycologists and 

 plant pathologists. The life history studies thus stimulated by de Bary 

 and his students have continued up to the present with so great a number 

 of investigators that mention of their names, even, must be omitted. 



The introduction of the recently developed cytological methods to 

 the study of fungus life histories began on a large scale with the investi- 

 gations by P. A. Dangeard (1894) in France, and of R. A. Harper (1896- 

 1897).. Their first publications along these lines appeared between 1894 

 and 1897 and were soon followed by the contributions of a host of other 

 eager students in all parts of the w^orld. The correction or confirmation 

 of previously held ideas — particularly with reference to the nature of the 

 sexual act in fungi — thus made possible, has proved to be of the utmost 

 value in assisting the determination of relationships among the fungi. 



In 1904 and succeeding years A. F. Blakeslee made known the occur- 

 rence of those sexual phenomena in the Mucorales to which he gave the 

 names heterothallism and homothallism. The study of these types of 

 sexual reaction has been extended to other groups of fungi: In the 

 Basidiomyceteae by Mile. Bensaude (1918), Hans Kniep (1913-1917), 

 Miss Mounce (1922), Vandendries (1923), Hanna (1925), and many 

 others from 1915 to the present; in the Ustilaginales by Bauch (1922), 

 Hanna (1929), Kniep, Stakman (1927), and others in the last twenty 

 years; in the Uredinales by Craigie (1927, 1931), Andrus (1931), Miss 

 Allen (1930), etc., since 1927; in the Ascomyceteae by B. O. Dodge 

 (1927), Ames (1932), Drayton (1932), and several others, mainly since 

 1927. Dodge (1928), Lindegren (1933), and others have made intensive 

 studies on the genetics of fungi in the last fifteen or more years, particu- 



