1)96 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of Grasses, viz. the Bromes, with the view of examining their anatomy 

 and histology in detail, in reference to the behaviour of the fungus in 

 their tissue. In course of time a series of phenomena came to light 

 which led me to go further into the conditions of infection, and to make 

 numerous experiments with the Uredo of the Brown Rust (Puccinia 

 dispersa), so common on certain species of this genus. These experiments 

 led to some unexpected results, and the purpose of the present paper is 

 to put together these results, since they appear not only of considerable 

 interest and importance by themselves, but promise to throw additional 

 light on some vexed questions of parasitism and immunity, and on the 

 relations between the host-plant and its invading or attacking fungus." 



The above may serve to show the general object of the paper, but it 

 must be said at once that it would be impossible by mere abstracts to do 

 justice to the various issues that are dealt with in this extensive work. 

 It falls under sixteen heads or chapters, ard there are twenty-eight tables, 

 many of them very elaborate and all of importance in the argument and 

 evidence with which they deal. There are practical bearings, and we 

 shall reach an important one at the end ; but let us endeavour first to 

 indicate the nature and great scientific interest of the investigation. The 

 author, in his work on Hemileia in 1881-82, the uredine which caused the 

 Coffee-leaf disease in Ceylon, was impressed by the probability, amounting 

 almost to a certainty, that the species Hemileia vastatrix on Coffee had 

 originated by the special adaptation of a certain species, Hemileia Canthii, 

 wild in the native forests on Canthium, to the cultivated Coffee. " Since 

 then Eriksson has elaborated a theory of adapted parasitism in connec- 

 tion with the rusts of our cereal Grasses, which has assumed a degree of 

 importance so grave, and so full of consequence for the understanding of 

 the epidemic diseases of cereals, that any investigations throwing further 

 light on the matter are welcome. Eriksson found, in fact, that the so- 

 called Rust of Wheat (Puccinia graminis) is a collective species the 

 morphological characters of which are now very thoroughly known, which 

 behaves differently according to the particular host to which it has 

 adapted itself as a parasite. For instance, if we take the uredospores 

 growing on Wheat and sow them on Rye, Barley, or Oats, the results are 

 negative. Nevertheless P. graminis occurs on these plants and forms 

 uredospores on them. If, similarly, the uredospores from Rye be sown 

 on Oats, the results are negative, whereas if sown on Barley they 

 infect it." 



" In other words, Puccinia graminis, while it infects all the above- 

 mentioned plants and preserves its morphological characters on all of 

 them, is so closely adapted to the particular host it happens to be on at 

 the time that the uredospores from this host can only attack successfully 

 and directly either this particular host or a limited number of its im- 

 mediate allies ; and the same specialised parasitism occurs in the case 

 of other species of Rusts growing on different hosts." 



" It thus becomes evident that we must modify our ideas considerably 

 as to the danger of infection of Wheat by the uredospores of P. graminis 

 growing in its neighbourhood on some other Grass. Further research 

 showed, for instance, that the uredospores of the fungus on the Weed Grass, 

 Agropyron repens, will infect Rye but not Wheat, and similarly with that 



