PROCEEDINGS 



OF THE 



(fewfoitrgc ^{rHflSopIjiral jforixtg. 



On the Question of " Predisposition" and "Immunity" in Plants. 

 By Professor H. Marshall Ward, D.Sc, F.R.S. 



[Read 20 January 1902.] 



Twenty years ago, in 1881-82, I expressed the conviction that 

 Hemileia vastatrix, the fungus of the Coffee-leaf-disease in Ceylon, 

 was an extended or adapted form of a native species of this 

 Uredine found on another host-plant, allied to Coffea, and be- 

 longing to the genus Canthium ; but although so convinced of 

 the essential morphological identity of H. Canthii and H. vastatrix, 

 all attempts to infect Coffee with H. Canthii and, reciprocally, to 

 infect Canthium with H. vastatrix, failed, and the germ of the idea 

 of adaptive parasitism fell to the ground. 



On the other hand, I was able to show that Hemileia vastatrix, 

 commonly supposed to be confined to Coffea Arabica, was capable 

 of infecting Coffea, Liberica, thus proving that the latter species 

 was not immune to the parasite. 



The questions which arose — but which were not then ripe for 

 such clear enunciation as they have since become — were, Have we 

 here a case, or cases, of differences of predisposition (susceptibility) 

 or immunity (resistance) on the part of the host-plants ; or is it 

 a matter of adaptability, or of failure to adapt itself to the new 

 host, on the part of the fungus ? 



Clearly both possibilities are theoretically to be expected, but 

 very little advance was to be made by speculation. 



The opinion has gained ground among planters, horticulturists 

 and others, however, that different races of cultivated plants differ 

 much in their susceptibility or predisposition to various fungi 

 which induce diseases, and in view of the facts brought forward 

 by those who grow such plants as Chrysanthemums, for instance, it 

 is impossible to overlook the significance of the case as one for 

 scientific enquiry. 



VOL. XI. PT. V. ^i<0 =! t !T!!= t==^ ^ 



flUL 8 1902V 



