578 STATE BOARD OF AGRICULTURE. 



attached to the plant, betray the presence of the disease, while the remainder 

 of the plant has all the appearance of a normal, midiseased indi\'idual. As 

 invasion progresses, more leaves may die and fall to the ground. The plant 

 takes on a general unthrifty appearance and, quite often, remains stunted 

 throughout its period of growth. In the case of severe attacks, plants top- 

 ple over, so completely are the crowns and roots destroyed. 



ON LEAVES. 



Under Michigan conditions, natural infection of the leaves has not been 

 noted, and if it does take ])lace it is probably of rare occurrence. Wherever 

 the disease has appeared in America, it seems to have been restricted to 

 underground parts. In literature and references pertaining to celery dis- 

 eases, there are only two citations of an occurrence of an organism of a Phoma 

 or Phyllosticta type on leaves of celery. Halsted (4) described a Phyllos- 

 ticta on celery leaves, which closely resembles the organism causing Phoma 

 Root Rot, and which produced a leaf-spot such as can be produced by inoc- 

 ulation, under the proper environmental conditions, with the root rot organ- 

 ism. 



In Holland, Klebahn (5) found the disease on celeriac leaves and on the 

 flowering parts, and also discovered pycnidia of the pathogen on the seeds. 



Given the proper conditions, the fungus is capable of attacking the leaves. 

 Sprajung with spores outside and in the greenhouse has not resulted in leaf 

 infection. Only a small amount of infection has been produced by spra3dng 

 the plants with a spore suspension and placing them under battery jars. 

 Much more uniform infection has been obtained by first germinating the 

 spores, then placing them on the leaves under small bits of wet cotton. On 

 leaves inoculated in this manner, signs of the disease began to appear after 

 two days. The results of infection may be of several kinds, depending on 

 conditions. If there is not too great a quantity of moisture present there is 

 first produced a light colored spot which later turns into an irregular red 

 blotch. Given more moisture, the fungus, possibly by the aid of other 

 organisms, produces soft, water-soaked areas, which are often studded with 

 pycnidia. In the first type of spot, fruiting bodies begin to be formed in 

 the mesophyll of the leaf, but seldom reach maturity unless the leaves are 

 subjected to exceptionally moist conditions. The progress of the disease 

 has been slow under all conditions maintained, and individual spots cease 

 to spread when the plant is taken out of a moist atmosphere, and more or 

 less normal relations restored. Leaves that have been killed by invasion 

 at the base, often show pycnidia on the petioles and blades, after remaining 

 on damp soil for a time, which indicates that the fungus is not selective as 

 to the part of the plant attacked, but is governed chiefly by environmental 

 factors. 



Inoculation experiments, and observations on the disease in the field, es- 

 tablish clearly that climatic relations in Michigan are not favorable to the 

 development of the leaf-spot phase. In no place, either in America or Eu- 

 rope, has leaf infection been reported as common'. The pathological signifi- 

 cance lies in the bearing which leaf and flower infection may have on the dis- 

 semination of the disease producing fungus. 



