BIOLOGIC SPECIALIZATION IN THE GENUS SEPTORIA 
23 
proves that the fungus has little adaptability. It may be possible, however, 
to obtain growth in some form upon the remaining species of Lepidium 
that have not been inoculated experimentally. 
Diagram 12. Infections with Septoria lepidiicola from Lepidium virginicum. 
Septoria helianthi Ell. & Kell. 
The following plants have been reported as hosts for Septoria helianthi: 
1. Helianthus grosseserratus 5. Helianthus petiolaris 
2. " annuus 6. " lenticularis 
3. " doronicoides 7. " strumosus 
4. " californicus 8. " laevis 
In the vicinity of Urbana this Septoria was a common parasite of H. gros- 
seserratus, upon the lower or shaded leaves of which it causes grayish-black 
spots that often become more than a centimeter in breadth. It was less 
commonly found upon H. tuberosus, upon which the spots were smaller, 
and rarely upon H. annuus and H. rigidus. 
In three separate trials H. grosseserratus was readily infected with its 
own form of Septoria without maintaining a humid atmosphere beyond 
three days. The other species of Helianthus infected by the Septoria 
from H. grosseserratus are shown in diagram 13. Except for H. tuberosus, 
which grcA^ naturally in the greenhouse yard, all these cross-infections were 
upon seedlings grown in the greenhouse. Proof of infection was obtained 
only by detaching spotted leaves and laying them in a moist chamber to 
induce the development of pycnidia. For this reason, as well as on account 
of the attack of insect pests, no accurate data could be secured concerning 
the degree of susceptibility of certain of the hosts, consequently some of 
the records are wanting. It is clear, however, that the original host is the 
only one that is congenial for this Septoria from H. grosseserratus, for on its 
