82 THE LOWER FUNGI— PHYCOMYCETES 



with a thick brown exospore and a thin hyahne endospore. 

 Germination occurs in the spring, both walls rupturing without 

 the extrusion of the endospore, and numerous swarmspores 

 being freed directly. If sexuality is concerned in resting spore 

 formation it has never been demonstrated. Another well known 

 species belonging to the subgenus Eusynchytrium is >S. fulgens 

 Schroter occurring on Oenothera. 



The best known member of the subgenus Mesochytrium is *S. 

 endobioticum (Schilbersky) Percival, cause of the much feared 

 and destructive disease of potatoes known as black wart (Fig. 17) 

 introduced into the United States from Europe (Orton 1919; 



Fig. 17. — Synchytrium endobioticum (Schilb.) Percival, cause of "black wart" 

 disease of potatoes. {Photograph by McCuhbin.) 



Hartman and McCubbin 1924). This species was made the basis 

 of a new genus by its discoverer Schilbersky, being named by him 

 Chrysophlyctis endobiotica Schilb. The genus was included by 

 von Minden (1911 : 228) in the Olpidiaceae where it was separated 

 from the other genera of the family by the strikingly angular 

 form of the resting spore. The position of the species in classi- 

 fication was for a time in controversy, but its inclusion by Percival 

 in Synchytrium has been justified by the results of more recent 

 research. The genus Chrysophlyctis therefore disappears. The 

 following discussion of the morphology and life history of the 

 species is based largely on the account of Curtis (1921: 409). 

 Her paper is of unusual interest in that she shows that the resting 

 spore in this species results from a sexual fusion of motile isoga- 



