BIOLOGIC SPECIALIZATION IN THE GENUS SEPTORIA 
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It appears significant that the Septoria from Helianthus rigidus did not 
infect H. grosseserratus when the plant, inoculated in the field, was bagged 
five days, and that the form from H, tuherosus did not give ready infection 
of H. grosseserratus in the greenhouse. The failure of infection in the series 
of inoculations made upon mature plants of various species of Helianthus 
on September 16 (table 4) in the greenhouse, and also on similar hosts in 
the field in summer, in which spores from H. grosseserratus were used, may 
have been due to the age of the leaves, yet checks on the original host gave 
positive results. A corresponding set of hosts were inoculated at these 
same periods with spores from H. tuherosus with negative results, but these 
were not shown by diagram as no checks were used. Still, in these cases 
the spores germinated well in laboratory tests. 
Diagram 13. Infections with Septoria helianthi from Helianthus grosseserratus. 
All the data obtained respecting Septoria helianthi indicate that the 
forms used in inoculation are not vigorously parasitic except upon their 
original hosts. These data are scarcely ample for definite conclusions, yet 
the results are in harmony with what was observed regarding the host 
range of this Septoria in the vicinity of Urbana. If there are no fixed 
