12 Research Bulletin No. p 



by the offensive odors of bacterial rots, producing a blackening 

 and softening of tissues which extends a considerable distance 

 beyond the actual site of the organism. Tin-, was demonstrated 

 microscopically and culturally. At times, however, especially 

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

 trichothecioides was produced. F. trichothecioides invariably pro- 

 duced a <lr\ fit 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 n<> 

 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. oxyspornm attacked the tissue intercellu- 

 larly at hrst, and then attacked the cells intracellularly. hut 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 

 i35). Manns (24), who report the occasional appearance of black 

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

 [ones (17), who attributes stem end rot <<i tubers U> 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 he 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 t<> determine whether or nut / ; . trichothecioides is unable to 



'■After these experiments had been concluded and this paper written, a 

 paper b\ Carpenter (7) has appeared. This represents a wholly independent 

 although simultaneously conducted piece of work. The results of Cadpenter 

 make 't 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 /■ oxysporum. 

 'lis conclusions as to the method of attack by the fungus and the nature of 

 the rot arc practically identical with (lie iter's. 



