FUNGOID PESTS OF CULTIVATED PLANTS. 61 



In this country its activities have been chiefly confined to the 

 Henbane, but. it evidently is on the alert "for all Solanaceous plants. 



The mycelium is abundant within the tissues of the plant before the 

 mould makes its appearance on the surface. The fertile threads are 

 rather robust, branching from five to eight times, in the upper portion in 

 a forked manner, with the branches spreading apart, and attenuated up- 

 wards, the final branchlets separating at a very obtuse angle, being short 

 and rather conical, each apex bearing a single spore, or conidium, of an 

 elliptical shape (13-24 x 18-18 /*) with a tinge of violet. 



Besting spores are probably produced on the mycelium, but at present 

 there is no evidence. 



It is .uncertain whether the conidia only germinate, or whether they 

 produce zoospores. 



Hitherto the species is recorded for Britain, Germany, Australia, and 

 North America. 



The only treatment suggested is spraying with dilute Bordeaux 

 mixture. 



Mass. PI. Dis. 81, 357 ; Gard. Chron. February 7, 1885, fig. 83 ; 

 Sacc. SylL vii. 877 ; Grevillea, ii. 139 ; Mass. B.F. 126. 



Another species (Peronospora dubia) is recorded on Hyoscyamus in 

 Austria. 



PETUNIA WHITE MOULD. 

 Eamularia Pettmia (Cooke), PI. IV. fig. 76. 



At present this mould must be considered as scarce, it having been 

 found only once or twice in this country on the leaves of Petunia. 



The spots are large, occupying nearly half the surface of the leaf, 

 somewhat circular in form, with a pale ochraceous tint. The conidia are 

 produced in considerable numbers at the apex of rather short undivided 

 colourless threads, which are more or less clustered on the spots. The 

 conidia are cylindrical, rounded at the ends, at first continuous, but at 

 length divided by a septum across the centre (20-22 x 4 /i). 



Wherever it has occurred this parasite has proved to be very destructive, 

 the spots sometimes extending over the entire leaf. No explanation can 

 be offered for its sudden appearance in the south of Britain, but it is 

 known that the moulds of this genus are very erratic, and, as a rule, 

 destructive. 



In the event of picking off and burning the diseased leaves not being 

 effective in checking the disease, it is recommended that diluted fungicides 

 should be applied, and for this purpose weak Bordeaux mixture may 

 be tried. 



Sacc. SylL x. 7294 ; Grevillea, vol. xx. 1891, p. 8. 



Other ordinary leaf-spots have been recorded on leaves of Petunia 

 abroad, such as Phyllosticta Petunia and Ascochyta Petunia. 



