102 DISEASES OF FIELD & GARDEN CROPS. [CH. 



cracks, and the contained protoplasm creeps out, as illus- 

 trated in the successive figures. First a small protuberance 

 is seen, then a slightly branched arm, next the main 

 growth is attenuated, then the attenuation proceeds to an 

 almost invisible hairlike tail or flagellum ; at last the 

 minute speck of protoplasm flies out of the - spore wall, 

 often whirling the empty case to some little distance. 

 Each atom of protoplasm which has emerged from the 

 spore is now a free zoospore, or animal-like spore capable, 

 aided by its hairlike tail, of creeping or sailing along, or 

 whirling round in any film of moisture, as illustrated in 

 the figures numbered from 7 to 12. 



These zoospores, like all other zoospores, do not long 

 remain in the zoospore condition. In most fungi zoo- 

 spores speedily burst and protrude a thread of mycelium ; 

 but in Plasmodiophora the zoospores quickly coalesce, and 

 when a few have conjoined they form the growth already 

 described as a plasmodium. The viscid plasmodium formed 

 by one set of conjoined zoospores speedily comes in con- 

 tact with other and similarly-formed plasmodia, and so 

 larger examples are formed. These examples, large and 

 small, are, when in a state of nature, washed out of de- 

 caying club-root material into the ground by the spring 

 rains. There, on and in the moist ground, they are able, 

 by pushing out arms and prolongations, and by con- 

 tinually propelling their contained vital material into 

 these extensions, to move about in a sluggish Amoeba- 

 like fashion. 



All practical agriculturists will now see that when 

 club - root refuse is left in the fields, or thrown on to 

 dung-heaps, and then distributed over the ground, the 

 most certain method is taken for propagating club -root 

 disease, for out of this decayed material innumerable 

 motile plasmodia will be washed into the ground. When 

 the seeds of turnips and cabbages grow and extend their 

 rootlets, the rootlets naturally come into contact with the 

 viscid watery plasmodia in the ground, and these plas- 



