DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 521 



mycelium penetrates the lemon rind and consists of much-branched 

 extensive hyphse of irregular diameter. Conidiospores which repre- 

 sent zoosporangia appear under favorable conditions. They measure 

 20 to 60 by 40/i to 90/i and are lemon-shaped with a pronounced protu- 

 berance at the apex. Upon opening a number of biciliate zoospores 

 are liberated. 



Infection of the fruit usually takes place in the orchard and also 

 during the operation of washing the lemons preparatory to packing 

 them. The wash water, therefore, should be treated with copper 

 sulphate, formalin, or potassium permanganate. In using formalin, 

 it is made up in one part to ten thousand parts of water, or i pint to 

 about 1200 gallons. Where the cheaper copper sulphate is more 

 available, i pound should be dissolved in 250 gallons of v;ater. 



Sooty Mold {Meliola Penzigi, Sacc, and M. camellia (Catt.) Sacc). — 

 This fungus is widely distributed in those districts where citrus fruits 

 are grown. It is most injurious to the orange, but occurs on the 

 lemon as well, appearing on both leaves and fruits. The mycelium 

 forms a sooty black covering on the leaves, twigs and fruits and is 

 usually associated with various scale insects and aphids, which exude 

 a honey dew upon which and the dead bodies of the scale insects the 

 fungus feeds as a saprophyte. The mycelium consists of large branched 

 threads, which are closely septate, and the branches are cemented 

 together to form a false stratum, which lives purely as a superficial 

 saprophytic growth without penetrating into the tissues of the citrus 

 plant on which it is found. Certain hyphal branches flatten out and 

 probably serve as appressoria. The reproductive cells are of various 

 kinds, such as stylospores in pustules, pycnidia with pycnidiospores 

 (pycnospores) and perithecia. The stylospores arise from small 

 conidiophores within peculiar, elongate, flask-shaped structures. The 

 pycnidia are small and scattered. The perithecia are spheric and in 

 close asci with eight dark elliptic, three- to four-septate spores. 



The most effective substance for the treatment of sooty mold has 

 been found by Webber to be the resin wash.^ The mixture consists of 



Resin 20 lb. 



Caustic soda (98 per cent.) 4 lb. 



Fish oil crude 3 lb. 



Water to make 15 gal. 



' DuGGAR, B. M.. Fungous Diseases of Plants: 215. 



