ROSELLINIA. 201 



propagated through the soil from plant to plant. There is a 

 resting-stage in the form of chambered sclerotia, black tuber- 

 like bodies which have their origin in the cortical parenchyma 

 of the roots and break out through the cortex, lleproduction 

 is effected throughout the summer by means of conidia, pro- 

 duced from a mycelium which vegetates on the surface of the 

 soil ; this mycelium bears conidiophores with whorled branches, 

 from which the conidia are abjointed. 



The perithecia are spherical structures composed of hyphae 

 with walls which swell up in a gelatinous manner. At first 

 the inside of the perithecium is a gelatinous mass containing 

 the paraphyses and the rudiment of the ascogonium. As the 

 asci are developed, they push their way into the gelatinous 

 mass amongst the paraphyses. Each ascus is a long club- 

 shaped tube, the apex of which is thickened and stains blue 

 with iodine, showing at the same time a canal piercing it. 

 The ascospores are canoe-shaped with sharp end.s, and when 

 mature have a dark brown colour. The spores germinate in 

 spring ; in water-cultures germ-tubes are emitted twenty-four 

 hours after sowing. The spores open by a longitudinal slit, and 

 a germ-tube emerging from each end branches into a mycelium 

 which soon takes on the form of a rhizoctonia-strand. Infection 

 takes place through the tender non-cuticularized apices of roots. 



The fungus may Ite combated if diseased portions of seed- 

 beds are isolated by means of trenches dug round tliem. If 

 boards soaked in carbolic acid or coal-tar are placed upright 

 in the trenches, greater certainty will lie secured that the 

 disease does not spread. 



Several species of Rhizoctonia , proliably related to tlu- above, 

 may now be briefly considered. 



Rhizoctonia violacea Tul.^ (U.S. America). Koot-fungus of 

 lucerne and clover. The presence of this disease is shown in 

 summer by the plants withering, and finally dying. The mycelium 

 lives inside the roots, and covers them externally with violet 

 coatings on %vhich the sclerotia appear as black tubers. 



On plants with sclerotia, Fuckel found pycnidia and peritlifcia of 

 Leptosphaeria {Trematosphaeria or Bi/ssothecium) circinans ; whetlier the 

 various forms were related could not, however, be determined. 



' Fostrup, Undersoerjtlser anijaaemle Svampeslae(jle» Rhiiodonia, 18S<). 

 Tulasue, Fungi hi/po(/aei, PI. IX. and XX., 1851. 



