x Obituary Notices of Fellows deceased. 
entire life history in from thirty to sixty hours at ordinary temperature. 
It forms long filaments, the growth of which Ward was able to measure 
under the microscope with great precision. On plotting out his measure- 
ments he obtained a regular curve, from which he found that, under 
constant conditions, the filament doubled itself in equal times. This he 
called “the law of doubling.” It is the same as the so-called “law of 
compound interest,’ and leads to the expression of the growing quantity 
as an exponential function of the time, so that the time is proportional 
to the logarithm of that quantity. This relation has, of course, long been 
familiar in chemical reactions, but, as far as I know, Ward was the first to 
detect it in any vital process in a plant. This, which was in 1893, has, I 
think, been overlooked. Stefanowska has since, in 1904, obtained a 
logarithmic curve for the early period of the growth of maize, which 
doubles its weight every ten days, and the subject has since been pursued by 
Chodat and others. 
In speculating on the cause of the destructive action of light on bacteria, 
Ward adopted the view of his friend Elfving, that it inhibited metabolic 
processes necessary to nutrition. He suggests that the “constructed 
metabolites” at the moment of assimilation are in a highly unstable 
condition, and liable to destruction by oxidation promoted by. hight. He 
points to the fact that plant structures are frequently provided with 
colour screens, which would cut off the blue-violet rays and check their 
action in promoting the rapid oxidation of reserve materials, and he quotes 
the suggestion of Elfving that chlorophyll itself may serve as such a screen 
against “destructive metabolic action in synthesis.” Ward seems to have 
attributed little importance to the fact that substantially the same view 
had long before been put forward by Pringsheim, though received with 
little favour. His own view that when red and orange predominate in the 
screens their effect is protective, has since afforded a probable explanation of 
the coloration of young foliage, especially in the tropics. 
It can hardly be doubted that the upshot of Ward’s laborious investiga- 
tions 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 Cambridge. He was 
supported by a distinguished body of fellow-workers, and developed a flourish- 
ing 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 
