106 FUNGOID PESTS OF CULTIVATED PLANTS. 



Onion Sclerotk. 

 Sclerotinia bulborum (Wakk.), PI. IX. fig. 135. 



This pest is liable to infest the bulbs of Hyacinths, Onions, and perhaps 

 other bulbs, and destroy a great number. Yellowish blotches appear on 

 the foliage in spring or early summer. These spots are soon covered with 

 an olive-brown mould. The mycelium passes down into the bulb, and 

 there blackish sclerotia are formed, from the size of a Mustard seed to 

 that of a Pea, within the scales of the bulb, and sometimes covering the 

 surface. 



During the following spring the sclerotia germinate and produce the 

 Peziza or Sclerotinia, the sporidia of which are binucleate (16 x 8//). 



It is recommended that the diseased bulbs should be burnt to diminish 

 the chances of dissemination from the germinating sclerotia. The further 

 measures recommended arc spraying with Bordeaux Mixture diluted on 

 the first appearance of the disease, or else the potassium sulphide solu- 

 tion. 



The brownish tufts of mould are compact, the tips of the fertile 

 branches spinulose, each spine bearing its conidium (9-10 x 7 /.<). 



Known hitherto in Germany. 



See also p. 69. 



Gard. Chron. xvi. 1894, p. 160, fig. 25 ; Mass. PL Bis. pp. 157, 380 ; 

 Sacc. Syll. viii. No. <s02. 



Onion Mucok. 

 Mucor subtilissimus (Berk.), PI. IX. fig. 136. 



The fungus about to be described is one of the kind known as Mucor, 

 of which a familiar example is known upon jams and decayed matter. 

 It is very rarely that they become parasitic. 



Many years ago Berkeley found on Onions a diseased condition about 

 the neck of the bulb, which was traversed by threads of mycelium, and 

 among them minute black bodies like grains of gunpowder. These 

 little bodies are compact, and of the nature of consolidated mycelium, 

 which we have already alluded to under the name of " Sclerotia." These 

 Sclerotia he found easy to germinate in water, and by this means he 

 discovered that they would produce fertile branches supporting little 

 globose heads. These heads are formed of a delicate membrane within 

 which are clustered a number of minute oval spores, which when they 

 are mature replace the membrane and escape. These spores themselves 

 will also germinate and produce a mycelium, which will combine and 

 form knots and become a new generation of sclerotia. 



By this means the secrets of this disease were discovered and its cause 

 attributed to the little Mucor subtilissimus, and the Sclerotium was 

 known as Sclerotium Cepavorum. 



Journ. Hort. Soc. iii. p. 9H, figs. 1-5; Cooke, Ildbk. No. 1898; -Sacc. 

 Syll. vii. 625 ; Mass. JJ. /'. p. 89; Smith, Field Crops, p. 51. 



For Onion Bacterial Rot see Journ. B.H.S. xxi\. p. 851. 



Of other Onion diseases we may name a smut which has evidently 

 escaped from North America and reached as far as Franco (Urocystis 



