160 FUNGOID PESTS OF CULTIVATED PLANTS. 



Turnips. Probably it is quite true that some of our vine-growers have 

 known it for years, but did not regard it in any serious light. 



The vine roots in question are swollen into large somewhat globose 

 nodules, as large as the fist, the surface being rough or warted, with 

 obtuse projections, and when cut the cellular interior is found to contain 

 a mucilaginous substance, not unlike the plasrnodium of some species of 

 Myxomycete. 



In all essentials the new parasite conforms to the Turnip club-root, or 

 " fingers and toes." In its earlier stages a section of the distorted root 

 will exhibit the ordinary cells enlarged to very many times their original 

 dimensions, and filled with a slimy mucilaginous fluid, of a yellowish 

 colour, capable of being drawn out into slimy strings, but with no trace of 

 the ordinary fungus threads, or mycelium, which usually accompanies 

 fungoid parasites. Later on, towards autumn and winter, the cells present 

 a somewhat different appearance, being no longer filled with the structure- 

 less mucilage, but differentiated into a host of nearly spherical bodies 

 with a distinct cell-wall, and possessing all the characteristics of conidia, 

 or fungus spores. These bodies are produced in enormous quantities, and 

 of an extremely minute size, but without colour. 



By patient research and continued investigation, it may be possible 

 to trace the germination and development of these conidia, which, it may 

 be presumed, do not differ materially from those of the Turnip club-root. 



In the slime fungi (Myxomycetes) the spores or conidia on germination 

 give origin to one, two, or more naked cells which possess the power of 

 movement, due to the protrusion of pseudopodia, or the presence of 

 a cilium : these are- known as swarm-cells. They possess a nucleus, 

 multiply by bipartition, and eventually coalesce to form a plasmodium in 

 this manner. After the production of numerous swarm spores by repeated 

 bipartition, little groups are formed, by the close approach of two or more 

 of these bodies : these groups often disperse again, but eventually the 

 components of a group coalesce, and lose their individuality. This 

 coalescence results in the formation of a small plasmodium which possesses 

 the power of attracting surrounding free swarm-cells, which at once 

 coalesce and augment the bulk of the plasmodium. This power of 

 aggregation and formation of a plasmodium originated the name of 

 Plasmodiophora, or " plasmodium-bearer," for the present genus, the 

 slimy mucilaginous stage being the plasmodium condition of the parasite. 



By a series of gradations it has been demonstrated that each atom of 

 protoplasm creeps out of its envelope and becomes a zoospore, with a kind 

 of hairlike tail. It may be conjectured how these creeping bodies, when 

 released from an old clubbing, remain in the soil, progress to other and 

 neighbouring roots, and thus continue to perpetuate and diffuse the 

 species. Each club root is therefore a centre from which the disease may 

 spread. It is scarcely probable that any of the numerous fungicides 

 will be of any avail to dislodge the parasite when once it has obtained 

 possession. The only feasible remedy is to extirpate by burning every 

 atom of infected roots, and not to plant again on the same spot without 

 removing the whole of the soil, and replacing it by fresh and unpolluted 

 earth. This may seem to be a drastic measure, but with such a foe only 

 measures which are thorough can be effective. 



