274 HARRY MARSHALL WARD 



screens their effect is protective, has since afforded a probable 

 explanation of the colouration of young foliage, especially in the 



tropics. 



It can hardly be doubted that the upshot of Ward's labo- 

 rious investigations has had a powerful influence in deciding 

 the policy of the future water supply of London. If we hear 

 nothing now of obtaining it from Wales, it is because we know 

 that even polluted flood-water if exposed in large reservoirs will 

 rid itself of its bacterial contamination, partly, as was known 

 already, by subsidence, but most effectually, as shown by Ward, 

 by the destruction of its most deleterious constituents by the 

 direct action of sunlight. 



In 1895, Ward was called to the Chair of Botany at Cam- 

 bridge. He was supported by a distinguished body of fellow- 

 workers, and developed a flourishing school, in which every 

 branch of the science found its scope. The University erected 

 for it an institute which is probably the best equipped in the 

 country, and in March, 1904, I had the pleasure of seeing Ward 

 receive the King and Queen at its inauguration. 



During the later years of Ward's life he returned to the study 

 of the Uredineae. 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 



