POSSIBLE SOURCE OF LEAF-SPOT DISEASE OF CELERY. 479 



Microscopical examination in the laboratory of the material which 

 was collected showed, however, that the fungus certainly was a Septoria, 

 and the appearance presented by the spores suggested strongly that 

 it was none other than Septoria Petroselini var. Apii, hence it was 

 recorded as such.* It is true that the spores, when measured, were 

 found to be rather larger than is usually the case when the fungus 

 grows on cultivated celery, but too much stress must not, I think, be 

 laid upon variations in the sizes of spores in such cases. I have found 

 considerable variation in size, particularly as regards length, in the 

 spores of this fungus on cultivated celery. 



According to Klebahn, the spores in Briosi's type materia are 

 from 22 />(, to 42 /A long. Saccardo says they are similar to those 

 in Septoria Petroselini, i.e. from 35 /x, to 40 ix. Chittenden gives 

 them as being from 38 to 42 /a, and in one instance I found them 

 from 36 /X to 49 /A in length. The spores of the fungus found on 

 the wild celery varied from 27 /x to 49 /x in length, and from 2'i /x 

 to 2-4 [X in breadth. 



No favourable opportunity occurred in 1913 for carrying out in- 

 fection experiments from the wild to cultivated plants, but during the 

 past summer the locaHty was revisited and fresh material collected. 



Infection experiments, with the necessary controls, were carried 

 out, both at the Temporary Station for the Investigation of Plant 

 Diseases estabhshed by the Irish Department of Agriculture at Qifden, 

 Co. Galway, and in the Department's Seeds and Plant Diseases Division 

 in Dubhn. At Clifden the plants of cultivated celery were in pots 

 sunk in the ground in the open air, while in Dubhn the experiments 

 were made in a greenhouse. Some of the plants were kept covered 

 with bell jars and some were not. 



Where water containing spores of the fungus from the wild celery 

 was appHed to the fohage of healthy cultivated celery plants, infection 

 occurred, but no sign of the fungus appeared on the control plants. 

 Moreover, the effect of the fungus on the cultivated plants was very 

 different from that seen in nature on the wild plants. The attack 

 was much more severe, and in fact resembled in every way the appear- 

 ance of the now, unfortunately, too well-known leaf-spot disease 

 on cultivated celery. The spots became enlarged in area and con- 

 fluent, pycnidia appeared in abundance, and the foliage underwent 

 decay, apparently as a direct result of the attacks of the fungus. 



The spores produced by the fungus when transferred from wild 

 to cultivated celery appeared to be somewhat reduced in size. They 

 measured in the latter case 20-43 x i*8-2-4 /x, the average being 

 32-4 X 2-1 /X. 



It was not possible to carry out the reverse infection, viz. from 

 the cultivated plant to the wild one, because it was impossible to 

 obtain wild plants on the foliage of which the fungus was not already 

 present. 



These infection experiments lead me to conclude that the fungus 

 * Irish Naturalist, xxiii. 1914, p. 48. 



