22 FUNGOID PESTS OF CULTIVATED PLANTS. 



POPPY ROT-MOULD. 

 Peronospora arborescens (Berk.), PL VI. fig. 15. 



This is the principal pest of the Poppy family, and occurs on the leaves 

 of the Opium Poppy, as well as on those of some uncultivated species. It 

 was first described by Berkeley in the JOURNAL R.H.S. forty years ago. 



It appears as a white mould, in patches, on the under surface of th& 

 leaves. 



The fertile threads are erect, slender, and divided from seven to ten 

 times, in the upper portion, in a furcate manner. The branches are more 

 or less flexuous and spreading, gradually attenuated, so that the final 

 branches are very thin, somewhat curved, and pointed. The conidia are 

 almost globose (15-22 x 13-18 /*), with a tinge of violet. In the autumn 

 resting spores are produced upon the mycelium, within the tissues of the 

 host-plant, and these are globose, with a striate brown envelope or coating. 



The production of active zoospores, and their aid in the perpetuation 

 of the species, follow the type of the other species of rot-moulds. 

 See Introduction, p. 2. 



This species has been found in France, Belgium, Germany, and Italy. 



Spraying as a remedy can be of little use in so deep-seated an 

 endophyte, but all parts of diseased plants should be burnt so as to 

 destroy the resting spores. 



Cooke Hdbk. No. 1785 ; Journ. Boy. Hort. Soc. I p. 31, t. 4, f. 24 ;. 

 Sacc. Syll. vii. 836 ; Cooke M. F. p. 217 ; Berlese Icones, t. xliii. ; 

 Mass. B. F. 120. 



A black mould, Heterosporium Eschscholtzice, is found on Esch- 

 scholtzia leaves in California. 



MIGNONETTE DISEASE. 

 Cercospora Reseda (Fckl.), PI. I. fig. J.6. 



This fungus is rather common on the wild species of Reseda, and 

 sometimes proves destructive to the cultivated Mignonette, causing dusky- 

 brownish patches upon the foliage. 



To the naked eye the blotches on the leaves seem to be minutely 

 velvety from the threads of the mould, and without definite margin, but 

 it spreads rapidly from plant to plant. 



The threads are short (50 p. long) and densely crowded together, 

 septate, and brownish in colour. The conidia are produced at the apex of 

 the threads singly, and are very long and flexuous (100-140x3 /*)> 

 attenuated gradually upwards, and divided by numerous (four to five or 

 more) transverse partitions, or septa ; they are also slightly coloured. 



It has been observed in Britain, Germany, Italy, the United States, 

 and Australia. 



Spraying with dilute Bordeaux mixture has been recommended. 



Sacc. Syll. iv. 2092; Mass.Pl.Dis. p. 319; U.S.A. Depart. Agric. 

 Rep. 1889, with plate ; Grevillea, iii. 182 ; Journ. R.H.S., xxix., p. 766. 



A rot-mould, Peronospora crispula, has been found on leaves of 

 Reseda luteola in the Rhine Provinces, and may at any time attack tha 

 Mignonette, should it appear on our uncultivated species of Reseda. 



