104 FUNGOID PESTS OF CULTIVATED PLANTS. 



ONION SCAB. 

 Vcrmicularia circinans (B), PL VIII. fig. 131. 



During some seasons this disease is abundant, while in others it is 

 scarcely known. 



It attacks the outer coating of the bulbs of Onions, and does them 

 very little injury so long as they are in the ground. It usually appears 

 when the bulbs are nearly full grown, under the form of scattered black 

 patches formed of small black velvety tufts, and these are arranged in 

 concentric circles or in irregular wavy lines. 



These tufts consist of quantities of erect threads, each bearing a long 

 slender slightly curved and colourless conidium or spore at its tip. 

 Besides which, the tuft is thickly studded with long black projecting 

 spines which gives it the velvety appearance. 



Has occurred in Germany and Italy as well as in Britain. 



The bulbs should be dry before storing, and none of the tainted ones 

 should be mixed. When the diseased bulbs are separated they may be 

 tried with a fungicide. 



Sacc. Syll. iii. 1376 ; Mass. PL Dis. 273, fig. 71 ; Gard. Chron. 1851, 

 p. 695, figs. ; Cooke, Hdbk. No. 1291. 



ONION SPINDLE MOULD. 

 Fusariella atro-virens (Berk.), PI. VIII. fig. 132. 



Berkeley has declared his opinion that the fungus above named is at 

 least one of the causes of the mildew which is so destructive to Onions 

 just before they arrive at perfection. The disease originates in little dot- 

 like spots with radiating threads, crowned with a greyish gelatinous mass ; 

 these at length unite, and the whole of the centre is occupied by the 

 spores ; the border keeps on increasing, and often quite fleecy, especially 

 if it meets with any impediment, but at length the whole mass is 

 greenish-black, and the border becomes obliterated. The threads of the 

 mycelium are white, and the spores are fusiform and curved, so as to form 

 about one third of a circle. There is one peculiarity in moulds of this 

 kind : that the spores seem to be held together for some time in a 

 gelatinous heap, and do not separate until they are quite mature, and 

 ready for diffusion. This peculiarity is rather an advantage, as it serves 

 to localise the attacks. 



Whatever fungicide is employed is of little import, so long as it will 

 destroy the parasite without injury to the Onion, and it is likely to prove 

 beneficial. Very little has been known of this disease for many years. 



Sacc. Syll. iv. 1876 ; Cooke, Hdbk. No. 1866. 



ONION EUST. 

 Puccinia Porri (Sow.), PI. VIII. fig. 133. 



Occasionally, for many years, this rust has attacked plants of the Onion 

 tribe and caused great trouble. In 1883 a crop of Chives was attacked 



