DISEASES OF UNCERTAIN ORIGIN 345 



mal cells contain the alga, which spreads over the leaf, 

 blackening and killing it. 



Karsten, Ann. Jard. Bot. Buiien., vol. x., i pi. (1891). 



Cephaleurus minus, Karsten, destroys the leaves of 

 Zizyphtis jujuba in Java. 

 Karsten, I.e. 



DISEASES OF UNCERTAIN ORIGIN 



(Rhizoctinia violacea, Tul.) 



This remarkable fungous parasite, the fruit of which is 

 not yet known with certainty, is too well known as being 

 most destructive to saffron {Crocus sativus). The roots 

 of many other plants are also attacked, including beet- 

 root, potato, lucerne, carrot, asparagus ; also many wild 

 plants. The tubers or roots are invested by a more or 

 less dense violet or brownish mycelium, which gives ofif 

 violet rhizomorphs that anastomose irregularly, and traverse 

 the soil, attacking adjacent roots. By this method the dis- 

 ease extends rapidly from a diseased centre, unless very 

 prompt measures are adopted. Two forms of sclerotia 

 are also developed, one kind being often as large as a 

 hazel-nut, and minutely velvety, the other small, glabrous, 

 and often densely crowded, resembling the perithecia of 

 some Rosellinia in general appearance. 



An ascigerous form of fruit — Leptosphaeria circi/ians, 

 Sacc— found on dead roots of lucerne {Medicago sativa) 

 killed by the Rhizoctinia, may prove to be the perfect form 

 of fruit, but this point is as yet undecided. 



Preventive Means. — If the disease appears, the area 

 should be isolated by a trench, throwing the removed soil 



