538 Journal of Agricultural Research voI.xii.no.? 



Florence, Sumter, and Charleston, S. C, and Wrightsboro, N. C. Accord- 

 ing to Clinton (8), the Fusarium-wilt of okra occurs in Connecticut. 

 Fusarium vasinfectum was not obtained by the writer from okra-wilt in 

 New Jersey; and VerticUlium alho-atrum was isolated from this host in 

 the South only in the few mentioned localities. 



V. alho-atrum was isolated from a wilt disease of the weeds AhutUon 

 sp. and Xanthium sp. in New Jersey ; and from spontaneous wilt of cotton 

 plants in rows adjoining the experimental plot at Arlington, Va. 



The wilt diseases of the several plants brought about by F. vasinfectum 

 and V. albo-atrum manifest the same symptoms, so that the real cause of 

 the trouble is safely to be determined only by cultural means. There is 

 a lack of turgor in the leaves first in evidence in those parts farthest 

 removed from the veins (PI. 20-23). The lower leaves are first affected, 

 wilt, and drop ofif one or two at a time. Frequently the plant does 

 not die for a long time, but continues a dwarfed existence. This is 

 especially true of the Verticillium-wilt. If the plants are cut longitudi- 

 nally and crosswise, it will be seen that the vascular tissue is brown or 

 black (PI. 18), the discloration being traceable from the small roots to the 

 top of the stem and into the petioles. Microscopic examination of thin 

 sections of this material shows that the vessels are plugged with the 

 mycelium of the parasite, which interferes with the conduction of moisture 

 to the aerial portions of the plant (PI. 17, E). The host tissues do not 

 appear to be invaded or broken down, the vascular inhabitant merely 

 living as a saprophyte on the fluids of the vessels, and injuring the host 

 plant only by mechanical obstruction of the latter. Whether there are 

 injurious products secreted in the metabolism of the fungus detrimental 

 to the plant in other ways is yet to be demonstrated. The parasitism of 

 these fungi is, then, a mechanical interference with the nutrition of the 

 host and not our usual conception of this term. 



METHOD OF TESTING PARASITISM 



In order to demonstrate the ability of V. albo-atrum and F. vasinfectum 

 to produce wilt diseases of okra and to gain a knowledge of the relation 

 of these organisms to other host plants, approximately i ,000 inoculations * 

 and cross-inoculations with pure cultures were made. Strains of V. albo- 

 atrum, isolated from okra, eggplant, potato, and snapdragon, were used 

 to inoculate okra; strains from okra, snapdragon, and eggplant were 

 used to inoculate eggplant; and the strain from okra was used to inocu- 

 late cotton. Similarly okra plants were inoculated with F. vasinfectum 

 isolated from okra and cotton ; and cotton was inoculated with this fungus 

 isolated from cotton and okra. 



The general method used in the inoculations may be summarized as 

 follows: Selected okra seed, or seed of other plants to be used, were disin- 

 fected in a solution of formalin, rinsed in sterile water, and planted in 



> The writer is indebted to Mr. J. M. R. Adams for faithful assistance in the inoculation tests. 



