316 Professor Marshall Ward, On the Question of 



In the annexed table (Table III.) I have put together the 

 results of 1846 infection-experiments with these pot seedlings, 

 arranged in such form as to show at a glance their significance in 

 the present connection. 



The results point without doubt to the conclusion that both 

 the source of the spores employed and the specific peculiarities of 

 the Brome inoculated are important factors in infection. For 

 instance, uredospores derived from B. sterilis successfully infected 

 B. sterilis in 68 cases out of 84 (81 °/ ), B. madritensis in 38 cases 

 out of 61 (62"3 %)> an d B. maximus in two cases out of 82 

 (2*4 °/ ), whereas they failed entirely to infect B. erectus [60 1 ], 

 B. secalinus [77], B. velutinus [71], B. arvensis [72], B. mollis [84], 

 B. racemosus [72], B. commutatus [72], B. interruptus [72], B. 

 Schraderi [9], and a number of others. 



Now B. madritensis is closely, and B. maximus distantly related 

 to B. sterilis, and all three come into the group Stenobromus. 

 The evidence goes to show that the spores produced under the 

 influence of the species of host B. sterilis (Stenobromus group) 

 have been so modified by the circumstances of their nutrition and 

 rearing, &c. that they can successfully attack other host-species of 

 the same (Stenobromus) group, but are unable to overcome the 

 obstacles to infection presented by the Bromes of the Festucoides 

 (e.g. B. erectus), Serrafalcus (e.g. B. mollis, &c), or Ceratochloa 

 (e.g. B. Schraderi) groups. 



Similarly with spores cultivated on B. mollis (Serrafalcus), 

 these attacked B. mollis successfully in 60 cases out of 85 (70'6 °/ ) 

 and other members of the same cycle of relationship (Serrafalcus 

 group) in proportions diminishing more or less with the closeness 

 of their relationship ; but only in one case out of 31 did a pustule 

 arise on B. erectus (Festucoides), and only in four cases out of 90 

 did infection succeed in B. sterilis (Stenobromus) as a consequence 

 of sowing spores from B. mollis on these species. 



Here arises the question, Is this a case of spores raised ok 

 B. mollis adapting themselves to B. sterilis and B. erectus ; or of 

 the latter proving individually less resistant titan their species 

 generally to the infection ? 



Even more striking were the results with spores which had 

 been reared on B. secalinus (Serrafalcus). They infected B. seca- 

 linus 16 times out of 16 trials (100 °/ ) and Br macivstachys 

 live times out of five trials, but were without result on B. inermis 

 (Festucoides) [5], B. sterilis (Stenobromus) [18], B. Schraderi 

 (Ceratochloa) [9], and so on ; and here again the only exception 

 to the generalisation that the spores from B. secalinus cannot 

 infect any Brome out of its oiun group Serrafalcus was a single 



1 These numbers in square brackets denote the number of attempts made. 



