638 STATE BOARD OF AGRICULTURE. 



arc not so clearly defined as tliose on tlie leaf. Tlie damage to the stem 

 i.s slight; Uiese sp(>ts do noj enlarge (o form cankers "and are not serious 

 except insofar as they i)roduce spores for further infection. 



Oil the Calyx: 



Small si)ols, nH)re or less elongaled, occur on the calyx and take a 

 form internu'diaie between Ihosc^ on Ihe leaves and stems. It may be re- 

 marked that (he dillereuces in form of the spot are doubtless due to the 

 texture of the host. 



On the Fruit: 



The disease has never been seen in Michigan as affecting the fruit in 

 the field, however, J. B. S. Norton, (1014) states, ''The disease may also 

 attack the fruit, causing dark spots." It will be seen later that artific- 

 ial inoculation with sjjores does not lead to infection of fruit, unless 

 the epidermis is ruptured. In general it may be noted that the damage 

 to the fruit by leaf-spot is negligible. 



ETIOLOGY OP THE DISEASE. 



Previous Work: 



H. C. Delacroix (1905) states, "In September, 1904, several attempts 

 at infection were made. The inoculation made on the leaves without 

 wound, simply by placing the spores on them, did not succeed except 

 when the surrounding air was thoroughly saturated, and under these 

 eircumstances, I was successful with but one infection. The eight which 

 1 tried to inoculate by a very slight scratch on the leaf gave better luck, 

 the infection resulting under these conditions were five out of eight at- 

 tempts." The only other recorded attempt to determine the pathogeni- 

 city of this fungus was performed by H. T. Giissow (1908). "A water 

 infusion of diseased leaf tissue spraj'ed on a healthy plant." "The whole 

 foliage, stem and young fruits were covered with spots." From the 

 meager experiments of Delacroix the impression that the organism is 

 merely a wound parasite would be justified while the experiment of Giis- 

 sow is inconclusive. 



Formal Proof of Causation: 



(a) Constant association of organism with the disease: 

 Suspected "leaf-spot" material w^as collected from Earliana tomatoes 



in the Botanical greenhouse. The typical spots were examined. Pycnidia 

 were found containing long, filiform, septate spores. Comparing this 

 material with descriptions of the fungus from various sources, the fun- 

 gus was diagnosed as Septoria lycopersicl Speg. 



(b) Pure culture: 



A pure culture was obtained by the ordinary dilution methods. The 

 material was carefully washed under a steady, fine stream of sterile dis- 

 tilled water. Pycnidia were crushed on a slide and plates w^ere poured. 

 These were incubated; later single colonies were transferred to nutrient 

 agar. Several days later, these Avere examined; pycnidia w^ere found in 

 abundance, but no spores were present. Portions of mycelium were 

 transferred to nutrient glucose agar, potato agar, and tomato agar. In 

 eight days pycnidia w^ere found containing typical, long, filiform spores. 

 Subcultures on the same media were made and spores produced in such 



