EXPERIMENT STATION BULLETINS. 595 



semination of the disease. The gelatinous matrix in which the spores are 

 imbedded necessitates a water distribution. When pycnidia are mature 

 and the spores pushed out in long tendril-like threads, the jelly-like matrix 

 is dissolved away leaving the spores free to be washed through the soil. 



The importance of this method of dissemination will depend largely on 

 the frequency of heavy rains and on the amount of surface drainage. When 

 the disease is present in the seed bed spores are disseminated by handling 

 plants at transplanting time. It is quite a common practice to take plants 

 from the seed bed and place the roots in water in a shallow pan until they 

 can be placed in rows in the field. Under such conditions a single diseased 

 plant, bearing pycnidia of the pathogen, would be capable of infecting an 

 enormous number of sound individuals. 



With an organism capable of living and growing for a period in soil, the 

 question of lateral dissemination by means of the growth of mycelium through 

 the soil must be considered. To gather experimental evidence on this point 

 plants in one side in each of five average size flats were inoculated in the 

 greenhouse and checks placed in the same flats at a distance of 4 to 12 inches 

 from inoculated plants. Watering was done with a sprinkler and the soil 

 was kept moist enough for a good growth of celery. After three months 

 the plants were pulled up and washed free from soil. Of the inoculated 

 plants 96 per cent were diseased; 2 per cent of the plants four inches from 

 inoculated plants were attacked, and all other uninoculated plants were 

 free from disease. Pot experiments and observations on checks used in 

 the greater part of greenhouse work have confirmed these results. It might 

 be pointed out that in the above experiments conditions were very favorable 

 for spread of mycelium as the soil was kept damp at all times. Due to its 

 oxygen relation the fungus can penetrate soil only to a short depth, and 

 since in the field surface soil is often dry the spread from plant to plant by 

 means of mycelium will assume even less importance than in the greenhouse. 



Varietal Susceptibility. 



The whole question of varietal susceptibihty is one which will require 

 more searching investigation and critical observation to solve the problems 

 here presented. Van Hook reports that Giant Pascal and Evans' Triumph 

 are much freer from the disease than is Golden Self Blanching. The most 

 destructive outbreaks of the disease in Michigan have been on Golden Self 

 Blanching celery, but unfortunately in these cases, no other varieties have 

 been present in the infested districts on which to make observations, or 

 with which to make comparisons. White Plume and Easy Bleaching are 

 known to be subject to attack under field conditions; other varieties have 

 such a limited use that data as to their relative resistance are not available. 

 The results obtained from the inoculation of a limited number of various 

 plants of various varieties, permit some decision in this regard. 



A variety test was conducted using Perle Le Grand, Smallage, Schumacker, 

 Dreer's Mammoth, Perfection, Easy Bleaching, Heartwell, Dwarf Golden 

 Heart, Winter Queen, Rose Ribbed Paris, Golden Self Blanching, Boston 

 Market, Columbia and Golden Heart. The method adopted for testing 

 these varieties was to place twenty-five plants of each variety in a separate 

 flat and thoroughly spray them with spores. 



Indications of infection first become apparent on Golden Self Blanching 

 and Golden Heart plants through a dying of the lower leaves and a general 

 checking of growth. In time, the same symptoms were to be noted on all 



