10 



H. H. Whetzel and John M. Arthur 



a, Long slender 

 hypha from the 

 region of the pe- 

 tri-dish culture 

 between sclero- 

 tial zones. The 

 characteristic 

 r hizoctonial 

 method of 

 branching and 

 septation is evi- 

 dent 



b, Profuse 



branching of the 

 young mycelium 

 in the sclerotial 

 zone. The bar- 

 rel-shaped cell 

 formation is 

 noticeable. This 

 mycelium is all 

 filled with dense- 

 ly granular 

 protoplasm , 

 with some vacu- 

 oles in the older 

 main hyphae 



1 



Figure 1. form and septation 

 of the mycelium of r. tuli- 

 parum from potato agar 



tonia species whose sexual stages 

 are known to be Corticiums (in 

 the sense of Burt, 1918) makes it 

 all but certain that, when found, 

 the perfect stage of S. tidiparitm 

 will prove to be a Corticium. 



Both Wakker (1885:25) and 

 Klebahn (1905:9) attempted to 

 obtain a fruiting form of the fun- 

 gus by overwintering the selerotia 

 in sand or soil. Neither succeeded. 

 Klebahn at least appears to have 

 expected from these selerotia the 

 production of apothecia. 



The writers' investigations seem 

 to warrant the transfer of the 

 fungus to the genus Rhizoctonia. 

 Although Schlechtendal's use of the name 

 Sclerotium tuliparum for Botrytis tulipac ante- 

 dates that of Klebahn, it appears legitimate 

 to designate this pathogene Rhizoctonia tuli- 

 parum (Klebh.) n. comb. 



Pathogenicity 



.Wakker (1885:24-25) concluded from field 

 observations that this fungus was the cause 

 of the rotting of tulip bulbs. He observed 

 also a fungus producing the same sort of 

 selerotia associated with a rot of hyacinths 

 and a rot of Di centra spectabilis. He made no 

 inoculation experiments with this fungus on 

 any of the three suscepts upon which he ob- 

 served its occurrence. 



The pathogenicity of this fungus on tulips, 

 however, has been fully established through 

 the careful inoculation experiments of Kle- 

 bahn (1905 and 1907). He (1907:28-29) 

 demonstrated that it may attack also 7m 

 hispanica, hyacinths, Fritillaria imperiales, 

 yellow narcissus, and Scilla sihirica, but on 

 these suscepts, except for the first, relatively 

 little injury and poor sclerotial formation 

 occur. Klebahn observed that the iris is 

 quite as severely injured as the tulip (1906: 

 564). He was unable to obtain infection on 



