PREFACE 



This thkatisk is part of a serios of leoturcs prc- 

 sfiitcd to srailuatc and rosi-arcli students of mycol- 

 ogy at C'oluniliia I iiivcrsity on tlif di'vi'lopnicnt. ori- 

 gin, and pliyloju'iiy of the lower fuiifri. It liad been 

 originally planned to incorporati' tliis material in a 

 general treatment of the simiile. hiHagellate Ooniy- 

 eete-like fungi. I.agenidiales, and Cliytridiales, hut 

 inasnnieli as tlie Plasniodiopliorales at present a])- 

 pear to lie a fairly eolierent iiliylogenetie group, it 

 seems advisable to treat them separately. The Plas- 

 niodiophorales are an important and significant 

 group of organisms from the standpoints of [ilant 

 pathology and phylogeny of the lower fungi. As de- 

 structive parasites of crucifers and potatoes, some 

 species cause serious economic losses of basic food 

 crops. Phylogenetically. they possess certain devel- 

 opmental phases which are strikingly similar to those 

 of the Proteomyxa. Myxoniycetes. and simjile fungi 

 — similarities which suggest either a common origin 

 or parallelism in development. 



Although the Plasmodiopliorales have been stud- 

 ied for more than a half century, no serious efl'ort to 

 summarize the accumulated data was made until 

 1<)33 when Cook monographed the group. Cook gave 

 a detailed description of the known genera and spe- 

 cies and also discussed their cytology and develop- 

 ment in relation to phylogeny. Unfortunately, this 

 otherwise worthy and excellent treatise is marred by 

 certain inconsistencies, based on the author's obser- 

 vations, which are confusing and misleading to be- 

 ginners in this field. Since that time, several new- 

 genera and species have been added to the group. 

 Particularly significant is the discovery of I.eding- 

 ham. Couch, et al.. and Barrett that the zoospores 

 are biflagellatc and heterocont and that thin-walled 

 evanescent zoosporangia are a characteristic devel- 

 opmental phase of the Plasmodiophorales. These 

 discoveries have greatly modified our concepts of the 

 group and make the present revision opportune, 

 worthwhile, and essential. 



This book is intended primarily for graduate and 

 research students of mycology and the lower organ- 

 isms. Nevertheless, botanists and biologists in gen- 

 eral as well as protozoologists and phytopathologists 

 will doubtless find the summarized data, life cycle 

 diagrams, and descri]>tions of diseases of consider- 

 able value. As a treatise for research students, it nec- 

 essarily includes nnicli that is questionable and con- 

 troversial in nature and which ordinarily might be 

 omitted or discussed more briefly. -Some of the data 

 presented are of doubtful value and significance, in 

 the author's opinion, but they are nonetheless in- 

 cluded with as little bias as possible in order that 

 students may draw their own conclusions and inter- 

 pretations. Although the author agrees with Cook 



and others that lihi-owi/ja, Sorolpidiiim, .-ind .liiiso- 

 mi/.rii are prob.-ibly synonyms of I.i</>iiiTa, these gen- 

 era are discussed separately as doubtful members. 

 Likewise, full treatment is given to the excluded 

 genera and s])ecies, thereby making these dat.i .ivail- 

 .■ible to research workers. The author's critical atti- 

 tude and seeming skejitieism toward existing data on 

 "akarvosis," extrusion of chromatin, sexuality, meio- 

 sis, and other critical developmental phases of this 

 group is not intended as a direct criticism of the 

 veracitv and accuracy of certain workers, but rather 

 to indicate how inconclusive present-day knowledge 

 and interjiretations are and thereby to stimulate 

 more intensive study of these phases. The Plasmodi- 

 ophorales are unfavorable for cytological study be- 

 cause of the minuteness of the nuclei. Likewise, the 

 intramatrical habitat of all species makes direct ob- 

 servation of gametic fusion, schizogony, etc., ex- 

 tremely diflicult in living material. It is therefore to 

 be expected that many data are conflicting and incon- 

 clusive. 



Separate bibliographies are provided at the close 

 of each chapter to expedite reference to literature 

 on particular subjects, genera, and species. Since 

 many of the cited papers are general in nature and 

 relate to several genera, they have been listed several 

 times, which makes the bibliograjjhy somewhat re- 

 dundant. A host index is also provided with each spe- 

 cies. Due to war conditions abroad, it has been im- 

 possible to secure many of the publications relating 

 to club root and powdery scab, so that the host index 

 and bibliography of Plasmodiophora Brassicae and 

 Spoiiflospora suhterranea are unfortunately incom- 

 l)lete. In a bibliograjihy of this magnitude errors are 

 likely to occur, and the author will appreciate having 

 mistakes and omissions called to his attention. The 

 glossary is purposely brief and relates almost en- 

 tirely to terms used in the text. 



Tlie writer has drawn freely from the illustrations 

 of authors in this country and abroad, to whom he is 

 very grateful. The list of contributors is too long for 

 individual mention, but full credit is given in the de- 

 scriptions of the drawings. The life cycle diagrams 

 presented in Chapters III and V have not been 

 copied directly from other authors' illustrations but 

 are based on their descriptions of the successive de- 

 velopmental phases. The author feels particularly 

 grateful to -Miss Amy L. Hepburn, Natural Science 

 Librarian of Columbia University, for her unstinted 

 help with the literature, without which this work 

 would have been impossible. 



Columbia Vnivkbsitv 

 New York City 

 No\t:mbkr. 19U 



