18 THE NORTH AMERICAN SLIME-MOULDS 



I. Plasmodiophora brassic^ Woronin. 

 1879. Plasmodiophora brassicae Woronin, op. c'tt. 



This species, typical of forms so far reported in this country, in- 

 fests the roots of cabbages,^ and produces a very serious disease of 

 that vegetable. In England the malady has long been known under 

 the names "clubbing," "fingers and toes," etc. The roots affected 

 swell greatly, and at length resemble sometimes the flexed fingers of 

 the human hand ; hence the English name. As the disease progresses, 

 the roots speedily rot away, to the serious injury of the leaf-bearing 

 portion of the plant. In badly affected fields, sometimes one-half of 

 the crop is utterly destroyed. Careful search continued through sev- 

 eral years has not availed to bring this species to my personal ac- 

 quaintance. 



For a full account of the parasitism of this species and its distri- 

 bution in the United States see Jour. Myc, VII., p. 79; also Bull. 

 66, Agric. Sta. of Vermont. 



Sub-Class EXOSPOREiE Rost. 



1873. Exosporeae Rostafinski, Versuch, p. 2. 



Spores developed, superficially, outside the fructification, wliich 

 consists of sporophores, membranous, or slender and branching ; spores 

 white, stalked. A single genus, — 



Ceratiomyxa Schroeter 



1889. Ceratiomyxa Schroeter, Engl. u. Prantl, I., i., p. 16. For further 

 synonj'my, see under first species. 



Sporangia none ; spores superficial, borne on erect papi^a^ or pillars, 

 or even on the inside of minute depressions or pits; each spore sur- 

 mounting a delicate pedicel or stalk. The spores on germinating 

 give rise to amoeboid zoospores, which undergo repeated divisions, 

 later become ciliate, and at length again amoeboid to blend into gen- 

 uine Plasmodia. At maturity the Plasmodium gives rise to numerous 

 minute divisions, each of which may lengthen in a direction perpen- 

 dicular to the surface and bear a spore at the tip. 

 1 For other crucifers, see Bull. Torr. Bat. Club, xxi, pp. 76-8. 



