650 STATE BOARD OF AGRICULTURE. 



source of iufectiou in the field. The possibility that Septoria lycoper- 

 sici may have some ascomycetous stage must necessarily hold in abey- 

 ance the problem of primary infection. It is very probable that part of 

 the infection, at least, is produced by pycnidia in the old trash. The 

 greenhouse or hot bed in which young ])lants are grown is an important 

 source of infection. Seeds are planted under glass three or four weeks 

 before they are set out in the field. Allowing five days for germina- 

 tion and appearance of the cotyledon there is a period of nearly three 

 weeks in which the fungus may spread. As has been shown the period 

 from the time of inoculation until the time of spore formation, is on the 

 average 13 days under favorable conditions. Thus at least one second- 

 ary infection is possible after the primary infection. This infection 

 usually shows as a series of spots about the older spot and is doubtless 

 due to the floating out of spores from the exudations of the first formed 

 pycnidia. Because of the comparatively long period between inoculation 

 and spore formation, leaves are frequently found with large blotches and 

 comparatively few pycnidia. These blotches with only a few pycnidia 

 might be mistaken for the lesions of Atternaria solani. 



The diseased cotyledons soon fall off and the plants are seemingly 

 clean but a latent colony may be present on the leaves. 



Numerous instances have been reported of the appearance of the dis- 

 ease in greenhouses in which tomatoes have never grown before. This 

 indicates the possibility of transferrence of the fungus on the seed. 

 Washings from tomato seeds have been centrifuged and examined re- 

 peatedly without successful results although the spore is characteristic 

 enough to enable recognition. 



It is believed, however, that the main source of infection is the trash 

 from a previous tomato crop. It has been repeatedly demonstrated that 

 rotation of crops diminishes the severity of Leaf-spot. If the infec- 

 tion came principally from the greenhouse, this rotation could hardly 

 be so effective. 



The agencies, aside from man, by which transferrence takes place are 

 mainly water, and wind. The matrix in which the exuding spores are 

 embedded holds the spores upon drying. These spores can be released 

 only when soaked and in this condition they may be washed down by 

 dew or rain. In culture pycnidia with exuding spores have retained 

 those masses for a period of 3 months without dislodgment or germina- 

 tion. After this time tomato plants were inoculated with a suspension 

 of spores and typical infection resulted. The matrix may have more or 

 less of an inhibitory effect on the spores. A mass of spores from a newly 

 formed exudate was placed in hanging drops but no germination result- 

 ed. Yet this retardation of germination may be due to the effects of the 

 spores on each other, a condition strikingly illustrated in heavily seeded 

 plates. (Stevens and Hall, 1909). 



The dew washes or floats the spores about on the leaf. This causes the 

 secondary infection which has been described. A large number of spots 

 on the leaf usually do not develop pycnidia before the leaf dies and 

 shrivels up. However, this dead, dried leaf which falls to the ground, 

 if kept at all moist, has been found to develop mature pycnidia and 

 exude spores more profusely than upon the living plant. 



The important agency in dissemination is the splashing of the rain. 



