274 Salmon, On Specializationof Parasitism in theErysiphaceae. 



In Exper. no. 59 tlie Oidium was sown on seedlings 11 days 

 old, of ß. molUs, on a potted plant of B. racemosus about 10 weeks 

 old, and on seedlings, 7 days old, of B. tectorum. Füll infection 

 resulted on B. mollis and B. tectorum^ while B. racemosus was 

 untouclied. 



In tlie next and last experiment with this Oidium (Exper. no. 64) 

 the fiuigus was again found to iufect fully B. mollis and B. tecto- 

 rum, while on B. velutinus the same behaviour as in previous ex- 

 periments was shown. On the 6 th day after inoculation, 1 leaf (of 

 the 4 inoculated) in one pot bore a few (about 10) conidiophores 

 Oii the under surface, and no trace of mycelium was anywhere ob- 

 servable; in the other pot minute flecks of mycelium appeared on 

 one or two of tlie inoculated leaves. On the next day, in the first 

 pot, the same Single leaf only showed a patch of conidiophores. (It 

 was noticeable, however, that all the inoculated leaves in this pot 

 showed signs of injury at the places Avhere the spores had been 

 deposited. This appearance was almost certainly due not to the 

 attacks of the fungus, but to some injury done to the leaves at the 

 time of sowing the spores). In the second pot a very few weak 

 mycelial patches and a very few scattered conidiophores appeared 

 on 2 of the inoculated leaves. On the 8 th day 2 leaves in both of 

 the pots bore a few scattered conidiophores; the control plants in 

 both pots remaining free. It appears, therefore, from the evidence 

 aftorded by these few experiments, that only ,subinfection' results 

 on the sowing of the present Oidium on B. velutinus. 



As a result of these ten experiments, which are summarized in 

 Table 1, it appears, then, that the Oidium on Bromus interruptus 

 {Serrafcäcus) is capable of infecting fully B. mollis and to a much 

 less extent B. brizaeformis and B. velutinus, — all belonging to the 

 section Serrcifalms; and also of infecting fully B. tectorum, of the 

 section Stenobromus; whilst it is unable to touch B. arcensis, B. 

 secalinus, B. racemosus^ B. commutatus, and B. macrostackys {ßerra- 

 fcdctis)] B. erectus, B. asper, and B. ciliatus {Festucoides); B. steri- 

 lis, B. madritensis, and B. maximus {Stenobromus) ; and B. unio- 

 loides {Ceratochloa). 



The next Oidium that was used was one that occurred on a 

 grass labelled , Bromus liordeaceus'- in the Cambridge Botanic Gardens. 

 This plant belongs to the section Serrafalcus, and is, as mentioned 

 above, probably B. mollis. This Oidium in the first experiment 

 (Exper. no. 2) in which it was used proved itself to differ biologi- 

 cally from the Oidium on B. irderruptus by causing füll infection 

 on B. commutatus, a species never touched by the Oidium on B. 

 interruptus. Tliis fact appears the more remarkable when we 

 remember that B. hordeaceus and B. interruptus are very closely 

 related. In this first experiment the Oidium on B. hordeaceus failed 

 to infect B. erectus, B. arvensis and B. asper. 



Sown again (Exper. no. 8) on B. arvensis and B. erectus the 

 same negative results were obtained. 



The Oidium was then sown on B. mollis, B. racemosus, B. 

 commutatus, B. secalinus and B. arcensis [Serrafalcus); B. sterilis 

 and B. maximus (Stenobrotnus) and B. erectus (Festucoides). In this 



