302 MR. H. MARSHALL WARD ON THE 
leia, germinating on the damp under surface of the coffee-leaf, 
emits a short, delicate tube which sends a prolongation through 
a stoma, and that the further development of this results in the 
production of the intercellular mycelium, a point of departure 
for further investigation was established. 
The presumption was fair, considering the analogies discovered 
between Hemileia and other parasitie fungi, that this ingrowth of 
the germinal tube is the true “infective ” act ; and I proceeded to 
ascertain if leaves on which spores were thus sown developed 
disease-spots, while others did not. Experiments made during 
the latter part of 1880 and the early months of 1881 established 
conclusively that this was the case. Having selected a number 
of seedlings which had been carefully grown under cover, from 
washed seeds, in baked earth, and which had presented no signs 
of disease, spores were sown on certain leaves of sixteen of the 
plants. 
The sowing in each case was performed as follows :—A large 
drop of water was caused to adhere to the under surface of the 
leaf, and in this suspended drop a number of the orange-coloured 
spores of Hemileia were carefully placed with a needle. A small 
glass chamber (formed by a glass ring, covered by an ordinary 
“cover,” and a piece of bibulous paper with a hole punched 
through the centre) was then clipped over the drop, and kept 
moist by means of blotting-paper on which a siphon was allowed to 
play slowly. All the plants were kept in a well-lighted, thoroughly 
ventilated room, of which the average temperature was 78^ Fabr. 
At various intervals, spores were carefully removed from one of 
the damp chambers and examined; the details of germination 
have been fully described elsewhere *. 
ALI the plants were watched day after day, and the leaves ex- 
amined to see if any “ disease-spots” appeared. At length 
“ disease-spots," or yellow patches, were seen to have arisen one 
after another, until fifteen of the infected plants had developed 
these normal symptoms of the malady. After carefully examining 
the whole experiment, and allowing a considerable time to elapse 
after the appearance of the first spot, I was driven to the following 
eonclusion :— 
The *disease-spot" was only developed on those leaves and 
plants whereon sowings of the fungus-spores were made; more- 
over, the yellow spot made its appearance only in the immediate 
* Quart. Journ. Micros. Sci., January 1882. 
