REED: SPECIALIZATION OF PARASITIC FUNGI 393 
It has repeatedly been suggested by many investigators that special- 
ized races of parasitic fungi may extend their normal host range by 
passing through certain so-called “bridging hosts.” There are many 
cases known where a particular host plant can be infected by two or 
more races of a parasite. Such hosts may enable a specialized race 
to infect a wider range of plants. 
Ward (172) apparently was the first to emphasize this possibility 
as a result of his studies of the behavior of Puccinia dispersa on various 
bromes. Ward supposed that Bromus arduennensis, which is readily 
infected with uredospores of Puccinia dispersa from Bromus mollis 
of the section Serrafalcus, as well as by uredospores from B. arduen- 
nensts of the section Libertia, served as a means for the rust on bromes 
of the section Serrafalcus to pass over on to bromes of the section 
Libertia. The following data indicate Ward’s results as bearing on 
this point. . 
Uredospores Uredospores 
from Bromus from Bromus 
Section Libertia: arduennensis mollis 
MST TIESUSEITE ALCTUIFETIS EUS ace oes. Se ASG NG It fein 0.5 SNS os Be 8/7” 13/14 
Bromus arduennensts var. villosus. 2.0.0.0 ce ee 10/10 1/14 
Section Serrafalcus: , 
SP ONUUSHINLOULUSP OA Mey Sti Ay es end Bie i a esl Oe wee 1/8 119/154 
BS TONUUSESCEQLINLUS Sol sa Seis aan ee Hh es 8/8 31/61 
Stenobromus: 
LER OURDSLDETE 0 Sea OE ee ee 0/6 1/74 
ES VONUUSESICNIIUSt A ASI Ay: poets hc sae ene s Mee nik Sane 0/8 4/148 
An examination of the above data leads one to conclude that the 
rust on the two hosts, Bromus arduennensis and B. mollis, are practi- 
cally identical in their capacity for infecting other bromes. The 
rust on Bromus arduennensis does not have any wider host range than 
the rust on B. mollis. Both grasses appear rather to be hosts for the 
same strain of rust. 
Ward’s evidence that Bromus Krausei and B. pendulinus may serve 
as bridging hosts is perhaps stronger. The following data indicate 
the relation of these bromes to the rust on Bromus sterilis and B. mollis. 
Uredospores Uredospores 
from Bromus from Bromus 
Serrafalcus: sterilis mollis 
IEF AOL OCIS OH TIS GT ste Cees a Oe a ee ae 14/29 27/27 
IBTOMUS PENAUIINUS.. oye Sc oe eee Vdd ea oe TFBS 50/50 
ESUONLISHTLOLLEL ORNL S ewe a a See a a ee ee 1/25 2/26 
SNOT SHIIVOLLES eae OTE Rosey SRS Ee So ce AE oi elem he 1/137 119/154 
BT OMUSLUCSTILUSTS ME A, SAA ono his Sal ties Jeo einer 1/4 3/4. 
Stenobromus: 
ESP OMLUESESUCEULES A APM At hots. gente athe ke Bee eva Loe 126/146 4/148 
ROLES IO Do, BORE SC OT cc Oe Or 37/60 6/53 
2 The denominator of the fraction indicates the number of leaves inoculated 
and the numerator the number infected. 
13 The denominator of the fraction indicates the number of leaves inoculated 
and the numerator the number infected. 
