96 DISEASES OF FIELD & GARDEN CROPS. [CH. 



and by the vital material from the mass repeatedly press- 

 ing into the arms or processes. The plasmodium is enclosed 

 by a dense hyaline layer, and this in turn is surrounded 

 by a thin coat of mucilage, which mucilage is sometimes 

 left behind by the progressing plasmodium like a trail of 

 slime from a slug. Although our fields are at all times 

 saturated and traversed by the spore contents or plasmodia 

 of this destructive fungus, yet Plasmodiophora has not 

 hitherto appeared in our printed lists or handbooks. 



The structure and habits of the members of the whole 

 family of the Myxomycetes, with its numerous genera, are 

 too involved and different from each other for any further 

 general description in this place. 



Clubbing commonly commences at an early period in 

 the life of the seedling turnip, cabbage, or other crucifer- 

 ous plant. If we take a young seedling turnip, one 

 which shows by its flagging foliage and dwindled growth 

 that it is out of health, and examine the root, we shall 

 probably see it, if attacked by the club-root fungus, some- 

 thing like the illustration at Fig. 34, which is engraved 

 one-half the natural size. The example illustrated repre- 

 sents a seedling turnip two months old. The rootlets 

 will be seen to be swollen with spindle-shaped swellings, 

 generally with a smooth and flowing outline ; and this 

 peculiar smooth spindle form of the clubs distinguishes 

 true clubbing from all abrupt tuberous swellings and 

 excrescences, sometimes natural, at other times abnormal, 

 as when caused by the insects and larvaa so common on 

 cruciferous plants. Every swelling in true club-root is 

 not necessarily perfectly smooth or truly fusiform or 

 spindle-shaped, but in the majority of instances, and 

 especially in an early state of growth, this distinguishing 

 mark holds good and is characteristic. Some entomolo- 

 gists have ascribed the origin of club-root to the attacks 

 of Aphides ; but Mr. G. B. Buckton, F.R.S., in his "Mono- 

 graph of the British Aphides," published by the Ray 

 Society, rejects this idea, but thinks some clubbing may 



