250 FUNGOID PESTS OF CULTIVATED PLANTS. 



are forked six or eight times. The final or ultimate branches are rather 

 short and pointed. The conidia are elliptical, rounded at the apex, and 

 of a pale dingy-violet colour (25-28 x 15-18/j). 



The resting spores are globose, and of a pale yellow-brown colour, 

 with a rough surface, the ridges forming a kind of wide meshed network. 



The life-history and transformation of this kind of mould are detailed 

 in the " Introduction." 



Known in France, Belgium, Germany, Finland, Italy, North America, 

 and Australia. 



Berk. Journ. Hort. Soc. i. 31 ; Sacc. Syll. vii. 819 ; Cooke, M. F. 1. 15, 

 f. 266, t. 10, f. 212 ; Cooke, Hdbk. No. 1779 ; Mass. B. F. p. 117. 



HOP MILDEW. 

 Spharotheca Castagnei (Lev.), PL XXIV. fig. 44. 



Although sometimes called Sphcerotheca Humuli, this pest is exten- 

 sively well known, and needs no description, as it is one of the worst foes 

 with which the Hop-grower has to contend. 



The first stage is that in which the leaves are invested with the dense 

 whitish felted mycelium, the erect branches of which become divided off 

 into conidia of the Oidium type, which fall on the leaves, and increase 

 their mealy appearance. 



Subsequently the globose receptacles appear scattered over the 

 mycelium, at first yellowish, and at length almost black, surrounded by 

 numerous appendages or flexuous threads, which are intertwined amongst 

 themselves or with the threads of the mycelium, and are somewhat 

 coloured. Each of these receptacles encloses but a single, nearly globose 

 ascus, or membranaceous cell, which contains eight elliptical and un- 

 coloured sporidia. 



This mildew is found nearly all over Europe, and wherever the Hop is 

 cultivated in Asia and North America. 



Sacc. Syll. i. 8 ; Cooke, M. F. p. 238, fig. 216 ; Mass. PI. Dis. p. 95 ; 

 Cooke, Hdbk. No. 1911. 



HOP SPILERELLA. 

 Spharella erysiphina (Berk.). 



This little parasite accompanies the Hop mildew and has only been 

 found associated with it. Probably, therefore, it inflicts little injury itself, 

 and will disappear with the mildew. 



The receptacles are minute and scattered, often superficial, and of a 

 brown colour, almost dot-like. They enclose cylindrical asci or vesicles, 

 which each contain eight colourless elliptical sporidia, divided across the 

 centre into two cells (12-13^u long). 



Sacc. Syll. i. 1975 ; Journ. Hort. Soc. ix. pp. 65, 67, 68, fig. 8 ; 

 Cooke, Hdbk. No. 2766. 



The Hop is also liable to become infested with the common Black 

 Mould, Fumago vagans, which is to be found on so many other plants, 

 and often accompanies the Honeydew. 



