EXPERIMENT STATION BULLETINS. 597 



placed out of doors over ^^inter. Two of these contained growing plants 

 which had been inoculated in midsummer and which were knowTi to be dis- 

 eased, in two others were diseased plants pulled from the soil and left on 

 the surface; two contained muck soil, mixed with sterile muck on which the 

 fungus was growing. In one flat diseased bases of plants were placed be- 

 tween layers of thick filter paper and covered with soil to depths varying 

 from 1 to 6 inches. April 1, 1920, the first six flats were taken into the green- 

 house and planted to celery. By May 1, the plants in the four flats con- 

 taining trash were showing signs of disease. The two flats containing soil 

 inoculated with a pure culture of the pathogen did not produce the disease, 

 indicating that under the conditions of the experiment the fungus did not 

 persist in the soil as a saprophyte. The diseased parts in the remaining 

 flat were examined for pycnidia and for a possible perfect stage. The lat- 

 ter quest was wholly unsuccessful, but pycnidia containing an abundance 

 of spores were found on nearly all diseased parts. These spores germinated 

 readily in tap water and indeed many of them had apparently germinated 

 between the layers of filter paper as masses of bluish mycelium were every- 

 where present. This mj^celium, after isolation, corresponded to that of 

 Phoma apiicola and produced disease when placed in contact with celery 

 plants. 



Before 1914 the greater portion of the celery seeds used in the United 

 States was growTi in Holland and France, where this disease is most destruct- 

 ive. As such seed importation is likelj'- to regain its former volume, it is a 

 question of first importance to determine whether or not the causal organism 

 is seed borne. 



Klebahn (5) found pycnidia of Phoma apiicola on the seeds and suggests 

 that seed distribution is important. Quanjer and Slagter (6) as stated be- 

 fore incline to the belief that infection from the seeds is exceptional. 



This latter view seems to fit in well with the facts as observed in Michigan. 

 The disease has, no doubt, been introduced from Europe on the seed or on 

 trash present with the seeds, but the occurrence of the fungus on seeds is 

 probably rare. Examination of French, English, and Dutch grown seeds 

 has not sho\^^l pj^cnidia to be present. The infrequency with which the 

 disease is found in the seed bed indicates that in the case of seeds shipped to 

 America from infested European countries introduction with the seed does 

 not commonly occur. While not often carried on the seeds, sporadic out- 

 breaks of the disease in one or two instances indicate that the seeds in some 

 cases may have been heavily infested. It is probable that seed carriage 

 is important in introducing the disease into new territories and in occasion- 

 ally being the source of bad seedling infections, but as a means of annual 

 distribution of the disease, it is probably of minor importance. 



Control. 



• Because of the fact that plants are attacked at a point located below the 

 surface of the soil, none of our common spraj's which are used to fight other 

 diseases of the celery plant are effective against this disease. Control meas- 

 ures must be based largely on certain relations of the disease to environmental 

 conditions and on the application of sanitary measures. In applying such 

 methods it is well to keep the foiloA\dng points in mind: (1) While some 

 varieties of celery are more or less resistant, none are known to be wholly 

 immune; (2) the disease may occasionallj^ be seed borne; (3) low tempera- 

 ture and high moisture content in the soil favor the production of disease^ 



