1909-1910-] Parasitic Moulds and Mildews. 1 99 



Cultivated Plants/ first published in the ' Journal of the Eoyal 

 Horticultural Society/ vols, xxvii.-xxix., and issued separately 

 in 1906; and De Bary's 'Comparative Morphology and 

 Biology of the Fungi, Mycetozoa, and Bacteria/ English 

 translation by Garnsey and Balfour, 1887. 



As the study of parasitic moulds and mildews has hitherto 

 been much neglected in Scotland, a list of some of the com- 

 moner and more notable forms observed in this country is 

 submitted, in the hope that it may have the effect of stimulat- 

 ing further interest in the subject. Most of the species 

 referred to appear to be widely distributed, and are probably 

 to be found in many localities within the Forth area. 



Phycomycetes. 



The endophytal parasites included in the Phycomycetes are 

 represented by five genera — viz., Cystopus, Phytophthora, Plas- 

 mopara, Bremia, and Peronospora. 



In Cystopus, each of the conidiophores terminates in a con- 

 catenate chain of conidia. These fertile hyphge are clustered 

 in dense groups or sori under the epiderm of the host, so as 

 to present when mature a conspicuous appearance as swollen 

 white blisters. The epiderm then ruptures and the conidia 

 burst through. In this genus, zoospores are developed both 

 in the oospores and the conidia. Three species may be noted, 

 viz. : — 



G. candidus (Pers.) Lev. — Abundant on many wild and 

 cultivated species of Cruciferse, such as Shepherd's-purse, Horse- 

 radish, Cabbage, &c., on which it forms conspicuous white 

 blisters containing the conidiophores. 



0. spimdosus De Bary. — Frequent on leaves of various 

 species of thistle, especially the Marsh and Lanceolate Plume- 

 thistles. 



C. lepigoni De Bary. — This appears to be uncommon, but 

 has occurred on leaves and stems of Sandwort Spurrey in 

 several localities on the East and West Coasts. 



The following four genera were formerly included under 

 Peronospora. They differ from each other merely in minute 

 microscopical details, and may therefore be conveniently treated 

 together. 



