116 M()KPII()I,<ii:Y WD |-.\H ASITISM IW lilll/oCTONIA. 



WDuld s(M'in licttri- to m,iii\taiii the (listiiutioii lu'twccn It. Snlmii 

 iiiid A'. M('<li<(i(/i>iis. 



( )f the earlier aocount.s of Rhizwlou'ia the l)est is that of Kiihii(l(i) 

 published in 1858. He mentions three species of Rhizoctonia — R. 

 solniii. R. medira(iluis and //. iidcnrnw. and gives a short 

 account of sclerotia I formation on the [)otato. contrasting the smooth 

 sclerotia of /'. sohaii with the woolly sclerotia of R. medicaginis ; 

 ill addition to iiiccine /.'. iiirilif<i(/i)iis is also stated to attack beet 

 and cairot. Kiihn dcsciilx's R/iizocloiiia as producing a reddish 

 ludwn coloiii in the cells of licet : he also gives figures of the hyphae 

 showiuii tlic characteristic mode of i)ranchiiig and the conjugation 

 of cells. This is tiic first iccord of tiie appeaiance of tlie fungus 

 in (Jermanv. all the pievious attacks having been in France ; from 

 now onwards the disease appears to have .spread rapidly in Europe. 

 Ill Denmark, between the years 188() and I!)0'2. it is recorded on 

 numerous iiosts. ('.(/.. cairots, lucerne, clover, sugar-beet and roots 

 of beech, pine and larch. In Sweden the jjarasiti.sm of the fungus 

 has been recently investigated by Erik.sson.(ll) His experiment.s 

 were directed chiefly towards the discovery of biologic forms of the 

 fuii'nis and showed that there was consideralile variabilitv in the 

 su.sceptibility of different varieties of the carrot to the di.sease. The 

 fungus which attacked the carrot would also attack the lieet, though 

 more viruleiitlv in the second generation, thus showing an increased 

 adaptation to the new host. In England ()iissow(14) has descnbed 

 the disea.se on potato and lucerne — he considers that R. solavi and 

 R. riolacea are one and the same. 



In America Rhizoctonia is known to attack much the same 

 crops as in Europe. Duggar and Stewart(l()) have descrilicd it on 

 a mimbei' of hosts ; they do not, however, give any details about 

 .sclerotia, but confine themselves to a description of the vegetative 

 hyphse, and it is. tlierefore. iinpo.ssible to determine from their account 

 whether one f)r several species of RhizoctoKia occurred on the different 

 hosts. The most interesting of the American ])ublications on Rhi- 

 zoctonia is that of Rolfs(24) who describes the morphology and 

 para.«itism of a species of Rhizoctviiiu on potato, A fruiting stage 



