LIFE-HISTORY OF HEMILEIA VASTATRIK. 319 
An instructive series of observations were made to obtain an 
answer to the guestion, How long will the leaf remain on the tree 
` when not attacked by Hemileia, and when only one or two small 
and barren disease-spots appear ? 
It was shown that leaves on which no disease-spots appeared 
commonly remained on the tree for 18 to 20 weeks and longer; 
Whereas leaves on which numerous spots were developed fell in 
6 to 11 weeks, or even sooner, after the unfolding of the buds. 
It may be imagined how differently two trees must be affected, if 
the leaves of one escape the ravages of Hemileia, and are per- 
mitted to work for the good of the tree during 18 to 20 weeks; 
while those of the other have to work (so to speak) for the benefit 
of the fungus as well, and yet persist but 6 or 8 weeks in all. 
Every degree of difference in these relations occurs in masses of 
diseased coffee, 
Having thus examined more or less in detail what occurs 
In laboratory experiments, and having drawn certain conclu- 
sions as to the behaviour of Hemileia when the chief circum- 
stances are under control, we may pass to the description of 
its behaviour in a state of nature, in the open, and see how far 
this is explained by the known facts. 
In proof that a “disease-spot” is formed exactly as before on 
coffee exposed naturally, I may cite the following experiment, 
which will also serve to illustrate other points of importance :— 
On December 23rd, 1881, a Wardian case was received from 
Jamaica, in which were eight living coffee-plants in bamboos 
containing Jamaican soil; in this rich dark mould flourished a 
dense mass of healthy roots, and each plant possessed a fair 
supply of vigorous leaves. 
Two of these plants were transferred to the open ground, being 
plunged into the soil without any disturbance of their roots or 
soil; these may be called A and B respectively. 
Two (C and D) were placed undisturbed in a cool shaded room, 
from which draughts of wind were carefully excluded. 
Two others (E and F) were placed untouched in another room, 
more exposed to light and air, and, like the rest, were watered 
regularly. 
A seventh specimen (G) was placed, also untouched, in a closed 
but light and well-ventilated Wardian case. 
The eighth plant (H) was placed in the same room as E and 
F, and under similar conditions. On the exposed plants A and 
B spores were scattered from a neighbouring “diseased” tree, 
252 
