THE FUNGI WHICH CAUSE PLANT DISEASE 387 



first seen in America in 1896 (Mass.) and soon spread over the 

 country. Numerous inoculation trials go to show that it is inde- 

 pendent of the other rusts common on nearly related Compositse.^ 



P. arenariae Wint.'"^ 



III. Telia compact, pulvinate, roundish, scattered, often cir- 

 cinate. Spores broadly fusiform or pyriform, summits pointed or 

 rounded, often thickened, base rounded or attenuated, slightly 

 constricted, smooth, pale yellowish-brown, 30-50 x 10-20 fi. 

 Pedicels hyaline, colorless, as long as the spores. 



A lepto-puccinia common on Dianthus. 



P. helianthi Schw. 



0. Pycnia clustered. 



1. iEcia in orbicular spots; peridial margins pale, torn; spores 

 orange, rarely whitish. 



II. Uredinia minute, round, chestnut-brown, spores globose to 

 ovate, 22-26 x 17-22 n, minutely spiny. 



III. Telia roimd, dark-brown to black; spores rounded at base, 

 slightly constricted, 38-50 x 20-27 /x, smooth; pedicel hyaline, 

 equal to or longer than the spores. 



Autoecious on numerous species of Helianthus, probably divis- 

 ible into numerous biologic forms. Imported from America to 

 Europe. 



Arthur ^"^ used fifteen species of Helianthus on which to sow the 

 teliospores of Puccinia helianthi produced on three species. The 

 results are given in table I on page 388. 



In the course of three years' work with this species sixty sowings 

 were made. 



"Looking over the table it will be seen that each set of spores 

 grew upon the species of host from which derived, but not upon 

 the other two species, except that spores from H. Icetiflorus sown 

 on H. mollis gave a tardy showing of pycnia, without further 

 development. Also each set of spores grew luxuriantly upon H. an- 

 nuus, and each made a feeble growth upon H. tomentosus, but on 

 all other species they either failed to infect or made a feeble growth, 

 with the single exception that spores from H. Icetiflorus grew well 

 on H. scaberrimus." P. Helianthi thus affords an example of a 

 single species having many races, for which H. annuus acts as a 

 bridging host. 



