596 STATE BOARD OF AGftlCULTURE. 



other varieties except White Plume and Giant Pascal. All inoculated plants 

 of these two varieties, upon examination, proved to be diseased; but the 

 characteristic symptoms were not to be seen on the parts of the plants above 

 ground. At the base, a thin ring of black diseased tissue showed that the 

 fungus was active, but was not seriously interfering with growth. In the 

 case of the other varieties there seemed to be no great difference in suscep- 

 tibility. 



As a result of these tests we feel justified in saying that though none of 

 the common varieties are immune to this disease, some give indication of 

 being more resistant than others. Golden Heart, Golden Self Blanching 

 and Dwarf Golden Heart, seem to be the three varieties which suffer most 

 from the disease. White Plume, Giant Pascal, and Easy Bleaching give 

 indication of being more resistant. These last three varieties are large, 

 rapid growing plants of a tougher texture. Herein probably lies the secret 

 of resistance. Succulent plants of any varietj^ are more susceptible than 

 plants of a tougher texture. Similarly different species of Umbelliferae 

 seem to correlate resistance with woodiness. 



Life History op the Casial Organism. 



In tracing the detailed life history of the parasite in relation to diseased 

 production, it is well first to consider the periodical development of the dis- 

 ease in the greenhouse and under field conditions. The first plant infec- 

 tion quite often came in the greenhouse or in the out-door seed bed in the 

 early spring. Clean plants of the first crop may be attacked after they are 

 transplanted to the field. The second crop or celery growing during mid- 

 summer is usually free from serious attacks. As the cool days of fall come 

 on, the Phoma root rot fungus again becomes active and may produce serious 

 damage in the last crop. 



There are several possible ways in which the causal organisms may pass 

 the winter; (1) in soil or trash of the greenhouse or in the cold frame; (2) the 

 refuse of the pre\'ious year's crop in the field ; (3) as a saprophyte in the soil ; 

 (4) on seeds, and (5) of course, there is alwa3^s a possibility, with an organ- 

 ism of this type, that there is an undiscovered perfect stage produced. As 

 to the first possibility the fungus is known to persist through one season 

 under such conditions. In case of the most serious outbreaks of the disease 

 at Kalamazoo, Michigan, the greenhouse was the location where infection 

 took place during two successive years and the point from which the disease 

 was carried to the field. The source of the organism for the initial infection 

 is unknown, but the appearance of the disease in a very virulent form the 

 second year points strongly to the fungus having lived over in the soil or 

 trash of the seed bed. In the greenhouse at the Michigan Agricultural Col- 

 lege, plants became diseased when placed in soil from around diseased plants, 

 after this soil had been kept in flats in the greenhouse through the winter 

 up to February. 



There has been some difference of opinion regarding the importance of 

 trash in harboring the organism. Klebahn is inclined to the belief that 

 seeds are very important in the distribution of this disease, while Quanjer 

 and Slagter minimize seed carriage and state that the chief source of in- 

 fection is to be found in the trash, manure, etc. To determine something 

 of the importance of trash and also to determine whether or not the organ- 

 ism lived as a saprophyte in the soil through the winter an experiment was 

 started September, 1919 on the following basis. Seven large flats were 



