PERONOSPORA 



ii5 



I tried Campbell's Sulphurator, three times as strong as we 

 usually use them (while the plants were still wet). This of 

 course literally whitened everything with sulphur. 



' Two days later I repeated this treatment, and although 

 this house had the disease very badly, I scarcely saw 

 another leaf fall. In fact leaves which previously would have 

 fallen at the slightest touch, now seemed firmly fixed to the 

 plants. I then applied this treatment to the other houses 

 with equally satisfactory results. The plants broke afresh in 

 a few weeks' time with quite clean foliage, since which I 

 have kept them clean with light doses of sulphur.' 



Tobacco mildew {Peronospora hyoscyami, De Bary) often 

 proves very injurious to the tobacco crop in different parts of 

 the world. In this country the fungus is not uncommon on 

 the henbane, from whence it might at any moment pass on 

 to allied cultivated plants belonging to the order Solanaceae. 

 Forming very delicate greyish-brown patches on the under 

 surface of the leaves. When attacked the leaves turn yellow 

 and droop. 



Conidiophores stout, tall, much branched, ultimate 

 branchlets pointed, straight, conidia elliptical, 15-24X 

 14-18 fi. 



Spraying with dilute Bordeaux mixture is said to prevent 

 the extension of this pest. 



Colocasia disease {Colocasia esculenta, Schott), one of the 

 Aroids, an important food plant in the West Indies, and 

 known by one or other of the following local names in 

 different islands, as 'Cocoes,' 'Tayas,' 'Tanias,' 'Tanniers,' 

 Eddoes.' 



The injury is due to a fungus called Peronospora tricho- 

 toma (Mass.), which attacks the tuber. In the early stage of 

 the disease, a tuber when cut across shows a number of 

 yellow dots or points, which correspond in position to the 

 vascular bundles; these become darker in colour as the 

 disease progresses, and finally the entire substance of the 

 tuber, with the exception of a thin peripheral portion, becomes 

 blackish in colour and decayed. At this stage the conidial 

 stage appears as a delicate, dingy white mould on the sur- 

 face, and oospores are abundant in the decayed tissue of the 

 tuber. The disease attacks the tubers after they are lifted. 



Mycelium thick, haustoria clavate ; conidiophores fasci 



