524 THE TATHOGKNIC SLIME-FUNGI. 



rind of compact plasma enclosing the spores, and frequently a 

 supporting skeleton or capillitium is present consisting of 

 numerous filaments of hardened plasma. 



Schroeter divides the Myxomycetes into three divisions, the 

 Acrasieae, Phytomyxinae, and Myxogasteres (including the Exos- 

 poreae and Endosporeae). Parasitic forms occur only in the 

 second of these groups. If, however, all the forms included 

 by Zopf in his group of Mycetozoa be taken into account 

 many of them will be found to act as parasites and to cause 

 frequent epidemics amongst algae and lower fungi. 



We shall here consider only the genera Plasm odiophora, 

 Tctramyxa, and Sorosphacra. The genus Phytoinyxa of Schroeter, 

 containing those micro-organisms which cause the root-tubercles 

 of Leguminosae, has already been considered in our general 

 part (see p. 101). 



Plasmodiophora. 



Spores spherical and developed inside the host-cells. This 

 genus causes diseases of considerable economic importance. 



Plasmodiophora brassicae Wor.^ This species attacks all 

 kinds of cabbage, kale, turnip, kohl rabi, and other varieties of 

 Brassica Papa, B. Napus, B. oleracea, and other edible Cruciferae; 

 also other plants from the same order, such as Ihcris vmhclIoM, 

 Capsella bursa-pastoris, MafMola incana, etc. 



The symptoms of the disease are manifold swelling, out- 

 growth, and branching of the roots at all stages of growth, 

 with a more or less marked stunting of the foliage, according 

 to the season of attack (Fig. 315). The forms assumed by 

 deformed roots are very variable and have gained the disease 

 many designations. In Britain it is known as " finger and 

 toe disease," " club-root," " clubbing," and " anbury " ; in Bel- 

 gium as "maladie digitoire " or " Vingerziekte " ; in Germany 

 as "Kropf" or " Kohlhernie." 



The disease was first recorded in Scotland about 1789, but 

 now it has a very wide distribution, appearing in all places 

 where cabbage, turnips, and allied vegetables are cultivated on 

 a large scale. The roots after swelling become rotten and 



^ Woronin, J^rinijahtima Jahrhurh, XI., 1878, p. 548. Eycleshynier (Jonriud 

 of Mycology, vii., p. 79) gives a good account of its distribution in America. 

 Massee, Transactions of Boyal Society of London, lvii., ISO."). 



