Harry Marshall Ward. x1 
Uredinexz. The scourge of wheat perhaps from the dawn of agriculture has 
been “ Rust,” 
“Ut mala culmos esset rubigo . . . . intereunt segetes ” ; 
and the loss inflicted by it throughout the world is probably not calculable. 
But the history of the Ceylon coffee disease is only too patent an instance of 
the injury a uredine can effect. 
Eriksson, the most recent authority on the subject, had found himself 
quite unable to account for sudden outbursts of rust which it did not seem 
possible to attribute to the result of infection. In 1897 he launched his 
celebrated theory of the Mycoplasm. He supposed that a cereal subject to 
rust was permanently diseased and always had been; that the protoplasm of 
the Uredo-parasite and of the cereal, though discrete, were intermingled and 
were continuously propagated together; but that while that of the latter was 
continuously active, that of the former might be latent till called into activity 
by conditions which favoured it. Ward discussed the theory in his British 
Association address at Toronto, and was evidently a good deal impressed with 
it, but nothing short of actual demonstration ever convinced him; and when 
he proceeded to investigate the actual histological facts on which the theory 
rested he promptly exploded it. 
It is interesting to note that Ward, as I know from correspondence at the 
time, had himself been embarrassed in investigating the Ceylon coffee disease 
by the same kind of appearance which had misled Eriksson. It is due to an 
optical fallacy. When the hypha of a uredine attacks a cell it is unable to 
perforate it with its whole diameter. It effects it, however, with a reduced 
and slender filament; this expands again after perforation into a rounded 
body, the haustorium. Ina tangential section the perforating filament cannot 
be distinguished, and the haustorium looks like an independent body immersed 
in the cell-protoplasm and with no external connection. It requires a 
fortunate normal section to reveal what has really taken place. Ward was 
accordingly able, in a paper in the ‘Phil. Trans.’ in 1903, to conclusively 
dispose of the mycoplasm. This cleared the ground of an untenable 
hypothesis. The complicated nature of the problem which still presented 
itself for investigation can only be briefly indicated. Sir Joseph Banks, whose 
scientific instinct was sound but curiously inarticulate, had pointed out that 
the spores entered the stomata, and warned farmers against using rusted 
litter. Henslow, one of Ward’s predecessors in the Cambridge chair, had been 
confirmed by Tulasne in showing that the uredo- and puccinia-spores (of the 
barberry) belonged to the same fungus. De Bary traced the germination of 
the spores and the mode in which the hyphe invaded the host; the 
fundamental fact, which he observed but did not explain, was that the germinal 
filament, after growing for a time superficially, bent down to enter the tissues 
of its host. Pfeffer in 1883 discovered chemotaxis, the directive action of 
chemical substances on the movement of mobile organisms. De Bary had 
previously hinted that the hypha might be attracted by some chemical 
ingredient of the host plant. Myoshi, a pupil-of Pfeffer’s, showed finally in 
