EDUCATION OF PARASITES 277 



varieties of Bromus, and had watched the degree to which they 

 were infected by rust under identical conditions. He found that 

 though in the brome-grasses the rust peculiar to them is specifi- 

 cally identical its forms are highly specialised. The form which 

 attacks the species of one group will not attack those of another. 

 Host and parasite are mutually " attuned." He termed this 

 " adaptive parasitism." This raised the problem, which had first 

 occurred to him in Ceylon, of how a parasite adapted to species 

 of " one circle of alliance " can pass to those of another. Occa- 

 sionally it happens that a uredo-form will infect a species where 

 it ordinarily fails. In such a case "its uredospore progeny will 

 thenceforth readily infect that species." Ward regarded this 

 as a case of education. Working on this principle, he succeeded 

 by growing the parasite successively on a series of allied species 

 which were imperfectly resistant, to ultimately educate it to 

 attack a species hitherto immune. He called these " bridgeing 

 species!' He established, in fact, a complete parallelism between 

 the behaviour of rust-fungi and that of pathogenic organisms in 

 animals. 



In the midst of this far-reaching research his health began to 

 fail. In 1904 he had been appointed by the Council to represent 

 the Royal Society at the International Congress of Botany held 

 at Vienna in June of the following year. This he attended, 

 though more seriously ill than he was aware of. On his way 

 back he spent three weeks for treatment at Carlsbad, but 

 receiving no benefit, he went, on the advice of Dr Krause, to 

 Dr von Noorden's Klinik at Sachsenhausen (Frankfort). Nothing 

 could be done for him, and he was advised to return home by 

 easy stages. After a period of progressive and extreme weak- 

 ness, borne with unflinching courage, the end came somewhat 

 suddenly at Torquay on August 26, 1906. He was buried at 

 Cambridge in St Giles's Cemetery on September 3. 



From 1 880, the year following his degree, Ward never ceased 

 for a quarter of a century to pour out a continuous stream of 

 original work. This alone would be a remarkable performance, 

 had he done nothing else. But he was constantly engaged in 

 teaching work, and he acted as examiner in the Universities 

 of London and Edinburgh. With no less conscientiousness he 



