1 86 Journal of Agricultural Research voi. v, no. s 



reinoculation were depended upon to check the work. In many cases 

 transfers of the original strains or of the reisolated ones, or of both, and 

 of any intruders were made to raw, sterile cut potato blocks. 



The identification of the closely related species of Fusarium employed 

 in this work involved the careful preparation, purification, and morpho- 

 logical study of high cultures. The nutrient media found of most value 

 in obtaining such cultures are as follows: Potato cylinders, rice, stems 

 of cotton (Gossypium spp.), and sweet clover (Melilotus alba). Agar 

 media were never used, except for plating. As emphasized by Dr. Wol- 

 lenweber, the vegetable media are very valuable for encouraging char- 

 acteristic development of species of Fusarium. 



The control tubers were carefully examined for rot about the wounds. 

 These tubers usually remained as sound as when placed in the incubator, 

 only 4 out of some 140 used as controls having any rot whatever. 

 Sprouting of the inoculated tubers and controls demonstrated their con- 

 tinued viability. 



Throughout the incubation periods a maximum humidity was main- 

 tained, and necessa: ly the ventilation was bad. Readings of the tem- 

 peratures were taken twice daily, and this factor is indicated by the 

 average of all reaJ.iijs obtained from the particular compartment dur- 

 ing the stated period. The temperatures were not constant, varying a 

 degree or two above snd below the average, but the average as recorded 

 represents very nearly the actual storage temperature, since such fluc- 

 tuations as occurred were of a temporary nature. 



It may be co^^s'^^red by some pathologists that the method is an 

 extreme one- *h^t ^nder the given conditions any organism might be 

 expected to cause a rot. It is believed, however, that the conditions 

 maintained are no more extreme than those to which potato tubers are 

 frequently subjected in f^eld and storage. The following facts tend to 

 establish the validity of the method: (i) Certain organisms — for example, 

 F. moniliforrne Sheldon, F. martii (sensu strict.), Verticillium albo-atrtim 

 Reinke and Berthold, and Sporotrichum flavissimum Link — did not cause 

 a rot under these conditions (see p. 201). (2) F. solani, F. vasinfectum, 

 a species of Mucor, and one of Rhizoctonia were doubtfully wound-para- 

 sitic (see p. 192). (3) The wounded controls remained sound except in a 

 few cases where they were in contact with badly rotted tubers; the 

 same organism was isolated from such controls as from the inoculated 

 tubers in the same compartment, (4) The species of Fusarium herein 

 reported as wound parasites grow and rot sterile cut potato blocks in 

 pure culture; none of the intruding organisms (bacteria or fungi) were 

 able to do this, except that in a few cases the submerged part of the 

 block was attacked. These facts, in addition to the experiments, seem 

 to warrant the conclusions reached. 



Since the tubers inoculated with the several species of Fusarium were 

 treated uniformly and the rots developed by the respective species were 



