380 REPORT OF THE CONFERENCE ON GENETICS. 
concomitantly with the specific morphological characters. Thus the 
species Bromus mollis, B. interruptus, and B. tectorwm have each a 
“ constitution’ rendering them liable to full infection by the fungus on 
B. interruptus, while B. commutatus, B. secalinus, Bb. racemosus, 
B. arvensis, and B. sterilis are all completely immune, and B. veluiinus 
partly immune, to the fungus in question. And similarly with respect to 
other “ biologic forms’ of the fungus (see Table). Such physiological 
or constitutional characters are constant and render the plant possessing 
them susceptible or immune in a definite manner, so that the various 
species of Bromus, according to their specific constitution—if one may 
use the term—behave differently to the attacks of the “ biologic forms ” 
of the fungus. 
We find further that two different plants which are so closely allied 
morphologically that they belong to one species differ constitutionally. 
Such a case, for instance, is supplied by the species B. commutatus and 
its variety racemosus. No trace of infection results when B. racemosus is 
infected with spores from B. commutatus, or vice versd. A further proof 
of the difference in constitution of the two plants is shown by the 
resistance of B. racemosus to spores from B. secalinus and B. hordeaceus, 
while B. commutatus is susceptible in both cases. 
The fact of the immunity of B. racemosus against so many “ biologic 
forms ”’ of the fungus (see diagram 1) is the more remarkable ongaccount 
G ay O. ce 
AO wml his yy bn wupoliz 
Ly / te 
ale 
ioe 
Aecahinnd 
Driacram I. 
In this diagram, and in the following one, the number of inoculations made 
and the results obtained are expressed in the form of a fraction, in which 
the numerator indicates the number of times in which infection resulted, 
and the denominator the number of leaves inoculated. 
of the existence on this species of a special “ biologic form ”’ which is able 
to infect it virulently. We see from this case how necessary it is for the 
scientific investigation of any supposed case of disease-resistance in a 
plant that a thorough study is made of the various forms of the fungus, - 
so that the exact degree of “immunity” can be ascertained. In the 
present case it would seem that plants of B. racemosus might stand 
among virulently diseased plants of B. commutatus, B. imterruptus, 
