828 MR, E. MARSHALL WARD ON THE 
The question is, W hat connexion had the weather, the presence 
of spores, and other circumstances with this definite appearance 
of two “leaf disease-spots ” on leaves which had been to all 
appearance perfectly healthy from April 25th to June Ist, 7. e. 
during some five weeks? It may first be stated that the weather 
from May 25th commenced to indicate the wet usually associated 
with the incoming of the south-west monsoon ; and wind and rain 
prevailed more or less up to the end of June, June 20th to 26th, 
however, being fine. 
The disease was first noticed on June Ist: if the * pin-spot” 
arose from the germination of a spore as I have described, this 
spore probably eommenced its action within three weeks or so 
previously. On comparing the notes made about the requisite 
period, two points are clear :—1st, there were spores being shaken 
and blown about at that time; 2nd, it rained heavily up to 
May 8th, and a series of hot, close, steamy mornings occurred 
thereabouts; and it also rained during the week preceding the 
discovery of the spot. It is evident, in fact, that an odd spore of 
Hemileia germinated (probably in the dew) on each leaf on or 
about the 16th-18th of May, and sent its tube into the leaf to 
form the mycelium of which the presence was discovered on 
June 1st-3rd. 
On June 15th the spot on the left-hand leaf was large and 
producing abundance of orange spores, which were being widely 
distributed by the high winds (from June 3rd to 15th), as well 
on surrounding trees and leaves as on other portions of the same 
leaf-surface. 
On June 29th many more disease-spots were apparent for the 
first time: these rapidly came to produce spores, and on July 1st 
numbered 35 new patches, each pouring forth hundreds of spores 
to be distributed as usual. The spores which produced these 
probably germinated about June 15th, in the showers so pre- 
valent during the month. By this time, also, the disease was 
bad all over the tree. I think it highly probable that the 35 new 
spots arose from spores detached from the one spot of June 3rd. 
By July 6th the leaf was badly diseased—the one older spot 
(of July 3rd) beginning to turn brown in centre, but still active 
in spores; the others, which might be termed the second genera- 
tion, shining through above with an orange hue. 
On July 15th there appeared about 12 new spots, evidently 
from spores which germinated during the wet week preceding 
