[ 186 ] 



®n tbe peronoepora^* 



By George Norman, M.R.C.S.E. 

 Plates 20, 21, 2 2, 23, 24. 



First Part. 



AMONGST the numerous groups of parasitic fungi that have 

 been investigated by mycologists during recent years, pro- 

 bably none, excepting the Bacteria, have received so much 

 attention as the two closely-allied ones of Saprolegnia and 

 Peronospora. These two groups have not only much in com- 

 mon between themselves, but as regards their development, etc., 

 are so closely connected with the Algse as to bear out the opinion 

 that has been expressed by some botanists, that the lower Algae 

 and Fungi pass into one another at one or more points. 



The Saprolegnie^ were fully treated of in the last Vol. of this 

 Journal,* and on the present occasion I propose to take up the 

 Peronospora in the same manner. The few species oi Peronospora 

 that were formerly known were at first included in the neighbour- 

 ing genus, Botrytis, but as fresh specimens were discovered, and 

 decided differences were thought to be observed between them and 

 Botrytis, a new genus was formed and called Peronospoi'a. This 

 genus now contains upwards of forty species. Peronospora belongs 

 to the family Hyphoniycetes, order Miicedmes, and the following is 

 Cooke's definition of the genus : — " Parasitic, threads mostly 

 inarticulate. Spores of two kinds. Conidia on the tips of the 

 branchlets. Oospores large and globose in the creeping myce- 

 lium." 



This definition is somewhat vague, and De Bary, who has 

 devoted much attention to this group of fungi, proposes to include 

 a far-removed group, Cystopiis, or White Rust, with the Pero?io- 

 spora, in one genus, and to subdivide them as follows : — 



I. — Cystopus. Conidiophores grown in large bunches, coni- 

 dia being developed in single rows in basipetal order. 



2. — Peronospora. — From a tree-like mycelium conidiophores 

 arise, singly or in small bunches at the ends of the branches, and 

 have no successors in the direct line. 



* See Vol. II., p. 185. 



