42 Ward. — Recent Researches on the Parasitism of Fungi. 
Bridging Species and their Significance. 
In 1903 (191, p. 145) I summarized the results of a long account of 
experimental work, as follows : — 
‘The table gives the results of nearly five thousand experimental 
infections made with the uredospores from eleven species of Bronius 
belonging to the three sections Stenobromus ( B . sterilis , B. diandrus , and 
B. crinitus), Liber tia (B. Arduennensis), and Serrafalcus (B. ar vensis, B. 
secalinus , B. mollis , B. intermedins , B. japonicus , B. patulus , and B. brizae- 
f or mis), on sixty-four species and varieties representing all the five sections 
into which the genus Bromus is sub-divided.’ I then gave the tabular 
results showing that in the vast majority of cases the uredospores from 
a given species of Bromus only infect the same species or, usually in 
diminishing proportions, species closely allied to it and in the same group. 
In the same paper (191, p. 139) I referred to some exceptional cases, 
which had occurred during the three years over which the experiments had 
extended, and on which I was at first inclined to lay no stress, regarding them 
as possibly errors ; but since they were found to recur, in certain species, so 
frequently, I was forced to conclude they had an important significance. 
Bromus erectus of the group Festucoides was once in thirty-seven trials 
found to take the infection from spores derived from B. mollis of the group 
Serrafalcits ; B. sterilis ( Stenobromus ) four times out of ninety trials by 
spores from B. mollis ( Serrafalcus ) ; B. Madritensis ( Stenobromus ) once out 
of thirteen trials by spores from B. secalinus ( Serrafalcus ) ; and B. maximus 
(Stenobromus) once out of seventy-four trials with spores from B. mollis 
(. Serrafalcus ) ; and I raised the question, ‘ Is this a case of species raised on 
B. mollis adapting themselves to B. sterilis and B. erectiis , &c., or of the 
latter proving individually less resistant than their species generally do to 
the infection ? * 
I then showed that the phenomenon turned out to be commoner than 
was suspected. 
Freeman (75), working in my laboratory, confirmed my previous results, 
and showed that in the case of five species infections occurred with spores 
both from B. sterilis and B. mollis as follows : — 
B. Gussonii ( Stenobromus ) was infected successfully thirty-seven times 
out of sixty with spores from B. sterilis , and six times out of fifty-three 
with spores from B. mollis ; B. Krausei ( Serrafalcus ) succeeded fourteen 
times out of twenty-nine with spores from B. sterilis , and twenty-seven times 
out of twenty-seven with spores from B. mollis ; B. pendulinus ( Serrafalcus ) 
twelve times out of fifty- three with spores from B. sterilis , and twice out of 
twenty-six with those from B. mollis. 
I then showed (191, p. 150) that B. Arduennensis of the group Libertia 
is not only particularly susceptible to spores from its own species, but 
