FUNGOID PESTS OF CULTIVATED PLANTS. 99 



Sacc. Syll. vii. 2204 ; Cooke, M. F. 194 ; Cooke, HdbJc. No. 1632. 



Diseases of Beetroot will be better treated in connection with Field 

 Crops. 



Spinach Black Mould. 



Heterosporiwm variabile (Cooke), PL VIII. fig. 124. 



The fading leaves of Spinach are liable to be invaded by a species of 

 black mould, similar to that which affects Carnations, which is by no 

 means so harmless as black moulds often are. The threads of the 

 mycelium take possession of the tissues, and the fertile threads finally 

 burst through the cuticle of the leaves. 



Definite rounded or irregular spots of a paler yellowish colour first 

 appear upon the still green leaves, caused by the mycelium of the fungus. 

 Then the surface of the spots becomes dotted with blackish points indi- 

 cating the threads of the fungus bursting through the cuticle. These 

 threads are flexuous, slender, knotted at the points and growing in small 

 tufts. Conidia are produced at the tips of the threads, simple at first, 

 then with one, two, or three divisions or septa (20-50 x 7-10 ^u). The 

 surface of the conidia is minutely rough with small spines. Threads and 

 spores are of a pale olive colour. 



When fully matured the conidia germinate freely at each joint, pro- 

 ducing a slender thread. 



Spraying with Bordeaux Mixture should be resorted to in order to 

 prevent dissemination of fertile conidia. 



Sacc. Syll. iv. 2310 ; Grevillea, v. 123. 



Spinach Rot Mould. 

 Peronospora effusa (Babh.), PL IX. fig. 125. 



The mould which attacks Spinach is of the same kind as that which 

 attacks Potatos, parsnips, and other vegetables. The pest appears upon 

 the living leaves in greyish, rather dense velvety patches, sometimes an 

 inch in diameter, and sometimes spreading widely over the leaf. The 

 mycelium is present in the leaf before the mould makes its appearance 

 on the surface. The threads are produced in abundance, issuing through 

 the stomates. The stem is undivided below, but in the upper portion it 

 is divided in a forked manner, from two to six or seven times, the final 

 branchlets being somewhat awl-shaped and arched. The ellipsoid 

 conidia occur singly at the tips of the branchlets (22-30 x 10-23 /j.) with 

 a dirty- white or slightly violet membrane. When mature thoy fall off 



readily. 



Resting spores are produced upon the mycelium within the tissues of 

 the plant, and are variable in size, of a bright brown colour, which is 

 irregularly furrowed and ribbed (25-88 /* diam.). 



Known in France, Belgium, Germany, Scandinavia, Finland, Austria, 

 Italy, and the United States. 



SaccSylLvii. 854; Gard. Chron. Ap. 11, 1885, fig. 87; Cooke, M. F. 

 f. 214; 215, Mass. PI. Dis. 79 ; Mass. B. F. 124 ; Berlese, Icon, slvii. ; 

 Cooke, Hdbk. No. 1781. 



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