On Specialization of Parasitism in the Erysiphaceae *). 



By 

 Ernest S. Salmon. F. L. S. (Kew). 



\ f I 



(With table XVIUand 6 images in the text.) 



It is Oüly quite recently that that specialization of parasitism 

 which results in the evolution of ,biologic forms' has been proved 

 to exist in the Erysiphaceae. In the Vredineae this pheno- 

 menon was originally discovered by Eriksson, and has been made 

 the subject of close investigation by several mycologists (8)2). 



In previous work dealing with the Erysiphaceae (1, p. 18, 

 6] and 2, p. 13) I have reviewed the scanty and inconclusive evidence 

 which existed up to the beginning of the year 1902 on the question 

 of the existence of ,biologic forms' in the Erysiphaceae. 



In January 1902, an important paper entitled ,Beiträge zur Biologie 

 der Erysipheen^ was published by Neger (4), in which a clear and 

 decisive answer was given to the above question. By numerous ex- 

 periments, of which details are given, Neger demonstrated the 

 existence of ,biologic forms' of Oidium belonging to several species 

 oiErysiphe. It will be of interest to enumerate these forms here, 

 leaving until later the discussion of other points mentioned in Neger 's 

 paper. 



The specialized forms investigated behaved as follows : — 



1. The conidia 0± Erysiphe Cichoracearum on Artemisia vulgaris 

 (Compositae) would not infect Senecio vulgaris, Leontodon 

 Taraxacum, Lactuca muralis, Artemisia Ahsinthium, Sonchus 

 oler accus, Hieracium murorum {Compositae); Lithospermum 

 arvense {Boragineae); Galium silvaticum [Rubiaceae); nor 

 Plantago lanceolata {Plantagineae) , — all of which species 

 have been recorded as host-plants of E. Cichoracearum. 



2. The conidia of E. Cichoracearum on Hieracium murorum would 

 not infect Sonchus oleraceus, Lactuca muralis, Artemisia vul- 

 garis, nor Galium silvaticum, — all host-plants of the species. 



3. The conidia of E. Cichoracearum on Senecio vulgaris would 

 not infect Hieracium murorum ; nor Symphytum tuberosum and 

 Pulmonaria officmalis {Boragineae), — host-plants of the species. 



*) Read before the Linnean Society, London, February 19, 1903. 

 2) These numbers refer to the works of authors given in the Biblio- 

 graphy at p. 32. 



Beihefte Bot. Centralbl. Bd. XIV. 1903. 18 



