X11 Obituary Notices of Fellows deceased. 
1894 that if a plant were injected by a chemotropic substance a fungus-hypha 
not ordinarily parasitic might be made to behave as such and attack it. 
In such circumstances it might seem that the host was not merely incapable 
of resisting invasion by the parasite but actually invited its attack. Nature 
is, however, not easily baftled in the struggle for existence. Attack provokes 
new methods of defence. Ward soon found himself face to face with 
“problems of great complexity,’ and these occupied the closing years of his 
life. 
It had been ascertained in fact that the rust fungus is not, as was at first 
supposed, a single organism, but comprises, according to Eriksson, thirteen 
distinct species, each with physiological varieties, and that those which 
are destructive to some grasses and cereals, are incapable of attacking 
others. This necessitated a scrutiny of the nature of grass-immunity. Ina 
paper communicated to the Cambridge Philosophical Society in 1902, Ward 
announced a conclusion which was as important as it was unexpected. 
He had more and more made use of the graphical method for presenting 
to the eye at a glance the result of a mass of separate observations. In 
this case he uses it with striking effect. He shows conclusively, as far 
as rust in brome-grasses is concerned, that: “The capacity for infection, 
or for resistance to infection, is independent of the anatomical structure 
of the leaf, and must depend on some other internal factor or factors in 
the plant.” 
Finally, he is led to the conclusion that “it is in the domain of the 
invisible biological properties of the living cell that we must expect the 
phenomena to reside.” He pointed out the probability that light would 
be thrown on this from the action of chemotaxis, on the one hand, and 
from that of toxins and antitoxins in animal organisms on the other. This 
is a most fertile conception, which would, however, have required a good 
deal of verification, and this, unhappily, he did not live to attempt. But 
with characteristic ingenuity he pointed out the analogy between the 
infective capacity of uredospores and the prepotency of pollen, which had 
previously engaged the attention of Darwin. In a paper published in the 
following year in the Berlin ‘Annales Mycologici, he announced a no less 
significant result. With his usual thoroughness in research he had 
cultivated side by side at Cambridge more than two hundred species and 
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 specifically 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. Occasionally 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.” 
