EXOSPORE^E 17 



infests 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 

 several years has not availed to bring this species to my per- 

 sonal acquaintance. 



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

 distribution in the United States, see Jour. Myc., VII., p. 79; 

 also Bull. 66, Agric. Sta. of Vermont. 



SUB-CLASS EXOSPORE^ Rost. 



1873. Exosporece Rostafinski, Versuch, p. 2. 



Spores developed, superficially, outside the fructification, 

 which 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 

 synonymy, see under first species. 



Sporangia none ; spores superficial, borne on erect papillae 

 or pillars, or even on the walls of minute depressions or pits ; 

 each spore surmounting 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 genuine plasmodia. At maturity the 

 plasmodium gives rise to numerous minute divisions, each of 

 which may lengthen in a direction perpendicular to the surface 

 and bear a spore at the tip. 



The homologies between the structures just described and 

 the fructification of the ordinary Slime-mould are somewhat 



