334 MR. H. MARSHALL WARD ON THE 
received at the outset the same guotum of disease-producing 
spores, which developed with equal energy and effect, and were 
equally related, actively and passively, in both examples. 
Or (b), if the above formidable details and their consequences 
be not assumed, it must be admitted that the various complex 
relations between coffee and its surroundings on the one hand, 
and Hemileia and its environment on the other, though differing 
in details in all possible degrees, amounted to the same final 
result in the two cases selected —that, although both trees were 
dissimilarly related in mass, vigour, &c., and in their quantitative 
and other relations to earth, air, light, and the fungus, &c., yet 
they became “ diseased ” in the end to the same extent. 
Either of the above assumptions would be rash in the extreme ; 
and no argument in favour of the view that some trees are pre- 
disposed to the attaeks of Hemileia can be logically based upon 
them. 
As a summary of the foregoing, it may be fairly considered 
proved that *leaf-disease ” here, as in so many other cases now 
known, is not antecedent to the fungus (Hemileia), but is conse- 
quent upon the injurious action of tbe mycelium ; the “rust”? 
and *disease-spots" are not mere signs of ill-health, due to 
obseure causes, but are preparatory stages in the spread of the 
disease-produeing parasite. This being so, no ground exists for 
considering the fungus as a “product of vitiated plant-life " or 
“of the sap ;" and just as little reason is there for the view that 
a sickly plant is prone to infection. Nay, experiments prove 
conclusively that a vigorous and healthy West-Indian tree is as 
easily infected as one from Ceylon; and it has also been shown 
that such a vigorous plant may produce more vigorous mycelium 
and spore-groups, 2. e. it may disseminate more of the disease- 
produeing fungus in a given period. 
Those who have the necessary knowledge of the physiology of 
such a plant as coffee, and can appreciate the changes produced 
by a disturbing agent such as the parasite, will not fail to see à 
vera causa for “ coffee-leaf disease” in the action of the fungus 
at many points for a long period. 
It may be asked, * How came the rapid spread of this fungus E 
The answer appears simply, having provided immense quantities 
of suitable food, carefully protected and preserved, man uncon- 
sciously offered just such conditions for the increase of this 
fungus as favour the multiplication of any organism whatever. 
