CYSTOPUS CONVOLVULACEARUM, Spec. 

 (Leaf Mould of Sweet Potato.) 



The disease has not been reported to occur in the West 

 Indies, but it is well-known in New Jersey, U.S.A. 



Pale spots appear on the leaves ; they are followed by- 

 brown patches which become darker in colour. On the 

 under side of the leaves a white mould is formed. 



Diagnosis : — Spots on both sides, small, dark coloured ; 

 acervuli white to pale-coloured, or light yellow, at first 

 covered by the epidermis, then erumpent to free, compact, 

 pulverulent; apical conidium slightly larger than the 

 others, all conidia globose-elliptical or globose-cubical, 

 15-20 by 12-13 microns, hyaline ; oogonia not seen. 



HALSTED : New Jersey Agric. College, Expt. Station, 

 Bull. 76, 1890. 



ASCOMYCETES. 



Perisporiace^e. 



UNCINULA SPIRALIS, B. & C. 

 (Powdery Mildew of Grape Vine). 



The disease was first observed in England in the year 

 1845, ar >d has since then spread over Europe ; it is identical 

 with the well-known mildew of the vine in the United 

 States of America ; it has also been recorded in Barbados. 



The leaves and grapes are attacked by the fungus ; 

 white spots appear on the infected parts and these become 

 later brown and withered. Withering of the infected 

 leaves soon occurs ; the grapes, however, continue to grow 

 at places which are not attacked until their coat ruptures, 

 and then they shrivel up. 



" Sulphuring " is the method of treatment generally 

 practised. It consists in dusting powdered sulphur over 

 the plant when it is threatened with attack. The sulphur 

 may be dusted by hand, but it is better to use a " puff.' ; 

 The operation should be repeated as frequently as possible. 



Diagnosis : — Mycelium arachnoid, amphigenous, often 

 evanescent ; perithecia minute, scattered, globose, blackish- 

 brown, appendages 10-20, variable in length, septate, 

 occasionally forked, tips loosely and spirally twisted, basal 

 portion coloured ; asci ovate, pedicellate ; spores 4-6, 

 elliptical, ends rounded, 20 x 8 — 10 microns. 



Masse : Text Book of PL Dis. p. 92, 1907. 



17 



