LIFE-HISTORY OF HEMILEIA YASTATRIX. 821 
December 23rd. Drizzling rain; cloudy afternoon; rainy 
night. 
December 24th. Cloudy, with sunny breaks. Cool. No rain. 
December 25th. Sunny and hot, with cloudy intervals. 
The germination must have occurred in these intervals. 
At various times experiments had been made to determine how 
the spores, which were observed germinating naturally on the 
coffee, arrived at their proper positions on the leaf. Careful 
observations on diseased coffee, made during gentle showers and 
steady breezes, convinced me of the following facts. Bearing in 
mind what an enormous quantity of orange “ rust," each grain of 
which is a spore capable of reproducing a “ disease-spot ” in less 
than three weeks, may be produced by one spot, and remembering 
also how easily these spores are detached, it seemed probable that 
the disease-spots produced later on a leaf might arise from spores 
shaken or washed from the earlier spots. 
If a perfectly clean glass slip, 3 in. x 1 in., be clipped on to a 
branch of coffee in the position of a leaf, in moist weather, two 
faets appear:—(1) spores, not only of Hemileia, but also of 
Spherie, Lichens, &c., may be observed on the slip in the course 
of several hours; (2) these and other small bodies tend to accu- 
mulate at the lower edges or tip of the glass, and even to travel 
to the lower surface and become suspended in the moisture pen- 
dent therefrom. 
That the spores &e. are washed, shaken, and blown into such 
positions aided by the action of gravitation cannot be doubted ; 
and this view explains why the earlier disease-spots on coffee- 
leaves, which have not been violently shaken, frequently appear 
at the edges and tips, subsequent spots appearing in the other 
regions of the leaf. These causes, combined with violent shakings 
during gusty and rainy weather, must contribute largely to dis- 
tribute spores from a diseased spot toa healthy part of a leaf, 
from one leaf to another, and even from tree to tree. But other 
observations prove that the wind conveys the spores of Hemileia 
through longer distances than the above. By exposing slips of 
glass, smeared with a thin layer of glycerine, in various positions 
in the neighbourhood of diseased coffee, it was shown that spores 
of Hemileia became entrapped in the glycerine; in one remark- 
able experiment the glass slips were exposed for 12 hours in a 
vertical position (the side smeared with glycerine facing the 
coffee) during a very high wind. The glass slip was 5 feet from 
