12 Research Bulletin No. g 



by the offensive odors of bacterial rots, producing a blackening 

 and softening of tissue which extends a considerable distance 

 beyond the actual site of the organism. This was demonstrated 

 microscopically and culturally. At times, however, especially 

 in cold, dry conditions, a dry rot as typical as that produced by F. 

 trichothecioid.es was produced. F. trichothecioides invariably pro- 

 duced a dry rot with only a very limited darkened zone extending 

 beyond the destroyed zone, made up of large cavities and a mixture 

 of disintegrated, dry, shrivelled tissue and fungus tissue. No 

 darkening extended beyond the actual site of the fungus and no 

 softening of tissue occurred. Microscopic examination revealed 

 the fact that F. trichothecioides attacked the tissue intracellularly" 

 and destroyed each cell completely before it proceeded to the 

 neighboring cell, while F. oxysporum attacked the tissue intercellu- 

 iarly at first, and then attacked the cells intracellularly, but not 

 until the tissue had been blackened and disorganized. In this way 

 a softened tissue without cavities was produced. These rots pro- 

 duced experimentally with pure cultures of F. oxysporum lend sup- 

 port to the observations and conclusions of Smith and Swingle 

 (35), Manns (24), who reports the occasional appearance of black 

 specks in the parenchyma of tubers infected with F. oxysporum, and 

 Jones (17), who attributes stem end rot of tubers to the activity of 

 this organism, although they may have dealt with "Mischarten." 

 Sherbakoff (33) reports certain strains of species of Elegans 

 (using the section as a morphological group) to be tuber rotters. 

 He distinguishes between Fusarium spp. that are tuber rotters and 

 such as are vascular element inhabitants. 1 



(2) EXPERIMENTAL INFECTION OF LIVING PLANTS 



A series of experimental inoculations of healthy potato plants 

 with F. oxysporum and F. trichothecioides were carried out, in an 

 attempt to determine whether or not F. trichothecioides is unable to 



1 After these experiments had been concluded and this paper written, a paper by 

 Carpenter (7) has appeared. This represents a wholly independent although simul- 

 taneously conducted piece of work. The results of Carpenter make it quite probable 

 that the observations made by the writer on a few strains of F. oxysporum are of 

 quite general application, since he arrives at the same conclusions for numerous 

 though different strains of F. oxysporum. His conclusions as to the method of attack 

 by the fungus and the nature of J:he rot are practically identical with the writer's. 



