150 PLANT DISEASES 



As already stated, the conidial form appears as a greyish 

 or brownish olive mould, often forming large patches 

 which, when examined under the microscope, are found to 

 consist of stout, erect, smoky-olive stems or conidiophores, 

 more or less branched upwards, the tip of each branchlet 

 bearing a cluster of broadly elliptical, colourless conidia. 

 The mycelium of the conidial form present in the tissues 

 of the host eventually forms numerous small black conidia. 



These sclerotia, after a period of rest, produce either the 

 conidial form of fruit, or the higher, ascigerous form. 



On the other hand, the spores of the ascigerous stage, on 

 germination form a mycelium, from which either the 

 Botrytis or the ascigerous form may eventually develop, 

 depending on conditions at present unknown. 



Preventive Means. — Spraying with dilute Bordeaux 

 mixture, or with potassium sulphide, destroys the conidia, 

 and thus checks the spread of the disease. Leaves and 

 fruit attacked by the fungus should be collected and 

 burned; otherwise, if allowed to remain lying about, the 

 sclerotia present in their tissues will eventually produce 

 spores, which will again infect the young foliage. 



De Bary, Morp. and Phys. Fungi (Engl, ed.), p. 224. 

 Pirotto, Nuovo Giorn. Bot. ItaL, vol. xiii. p. 130 (1881). 

 Vial a, Les Maladies de la Vigne, p. 352, figs. 



SCLEROTIUM DISEASE 



{Sclerotinia scleroiiortim, Massee. 

 = Sclerotinia libertiana, Fuckel.) 



Probably no other parasitic fungus attacks and kills so 

 many plants of different species, and belonging to widely 



