CAUSE AND NATURE OF CROWN-GALL 



39 



Fig. iS. — Photo-micrograph of isolated wooded nodules from the surface region of a 

 fair-sized gall (X 20). 



THE CAUSE OF CROWN-GALL. 



The cause of crown-gall appears to be a specific organism, be- 

 longing to the slime-molds, or Myxomycetes. Altogether about 

 200 species of slime-molds have been published as occurring in 

 North America. Of this large number but a single. species is 

 known to be parasitic, and this is considered by some authors 

 as a doubtful Myxomycete. The parasitic species heretofore 

 described is the common Plasmodiophora brassias, which causes 

 the disease known as " club-root " in cabbage and allied plants, 

 which was worked out and described by Woronin 3 ' in 1876, 

 and which has in recent years been studied in this country by 

 Eycleshymer. 33 It is also described at some length and figured 

 by Sorauer 34 and Tubeuf. 35 



3 -Prings., Jahr. f. wiss. Bot., Vol. XI, 1878. 



33 Jour. Myc, VII, 79. 



34 Handbuch der Pflanzenkraukheiteu, II, 66 (1896). 



•'•' Diseases of Plants Induced by Cryptogam ic Parasites (English trans- 

 lation, W. G. Smith), p. 522. 



