FUNGOID PESTS OF CULTIVATED PLANTS. 



45 



Hitherto resting spores have not been found, although there is no- 

 doubt of the relationship of the species to the rot-mould found on 

 Hellebore, Anemone, and other plants. 



Reference to other rot-moulds, of the genus Peronospora, will show 

 the kind of treatment recommended. See Introduction, p. 3. 



This species has made its appearance also in Germany and the United 

 States of America. 



Sacc. Syll. vii. 884 ; Cooke M. F. 161, 287 ; Berlese Icones. pi. Iviii. ; 

 Gard. Chron. 1862, p. 308; Cooke Hdbk. No. 1790; Tubeuf, Dis. 

 133, fig. 



ROSE MILDEW. 

 SpTicerotheca pannosa (Lev.), PL III. fig. 54. 



Very little description is needed of this very common and well-known 

 disease, which clothes the leaves, twigs, and flower-stalks of all kinds of 

 Roses with a dirty- white felted mycelium of interwoven threads, distorting, 



FIG. 5. (1) Eose Leaf, blotched with the Mildew. (2) Chains 

 of Conidia. (3) Conidium germinating. 



blighting, and spoiling the Roses, to the great disgust of the gardener, 

 and almost drives him to despair in the face of his helplessness. 



This is really an epiphytal disease, and makes its appearance externally 

 before it invades the tissues. In its first and earliest stages it is a white 

 mould called Oidium leucoconium, and is of a kindred with the Oidium 

 Tuckeri, which affects the Vine. 



In the conidial or oidium stage the profuse mycelium sends up short 

 branches, which produce the oval conidia attached to each other, end to 

 end, in a chain (20-30x13-16^) when mature : these separate at the 

 joints, and fall away, each to germinate on its own account. 



The more perfect condition of the disease is the stage in which little 

 blackish points or globose receptacles appear scattered about upon the 

 whitish mycelium. These receptacles are at first pale, but soon become 

 of so dark a brown as to appear black. These receptacles adhere by little 

 filaments to the mycelium, accompanied by free floccose appendages 

 which do not adhere. The receptacles are composed of an outer coloured 



