AND LIFE-HISTORY OP ENTYLOMA RANUNCULI. 
175 
runs off rather slowly to the south. A fairly dense growth of hazel and other trees 
overshadows all, and in the summer but little sunlight reaches the plants in the 
ditch after noon : the morning sun nevertheless reaches the plants under and through 
the trees during the earlier months named. One consequence of all this is that the 
leaves of the Ranunculus were very succulent, bright, and long-stalked, and, as 
already mentioned, appeared to fill up the hollow of the ditch. 
Towards the middle of April the bright green glossy leaves of the Ranunculus 
plants in a certain part of the above patch were noticed to be slightly spotted with 
white flecks, which increased in size and number day after day until before the middle 
of May a long tract—several yards—of the thickly growing leaves were infected and 
thus spotted. 
Before describing the phenomena more closely, and simply speaking of the white 
flecks as the chief obvious symptom of the diseased condition, I may call attention to 
one or two points which seem significant. Ranunculus Ficaria is an extremely 
common plant all over the neighbourhood of Englefield Green, and nevertheless I have 
failed to find the white spots on leaves in many places near. Nor is this all; 
hundreds of plants on the eastern side of the garden (the ditch runs along the 
western side) have been examined, and no traces of the spots found, and even in the 
ditch referred to none of the plants in the northern two-thirds of its length were 
spotted as described. The disease—the epidemic, I will say—commenced on a few 
plants in April, and spread southwards for several yards during April and May. I 
account for this as follows :—The easily spread spores (conidia) of the fungus causing 
the disease were transferred by wind, and especially by water flowing southwards in 
the ditch during the rains occurring at various periods in April : the wind, as I had 
occasion to notice, was chiefly from the north and east at these times, hence the 
immunity of the plants in the northern parts of the ditch and on the other side of 
the garden. Even the fact of a south-west or west wind occasionally does not 
contradict the conclusion when all the circumstances are known, for a high bank and 
hedge lie to the westward of the ditch, and the hazel trees mentioned above would 
screen other parts of the garden. 
An extraordinarily severe outbreak of the white spots occurred over the patch during 
the period May 6th to 12th, and it was then I noticed particularly how the epidemic 
spread to the south, and not to the north; the period referred to was remarkable for 
very warm “ steamy ” mornings and very bright noons. A storm broke over Engle¬ 
field Green on Saturday, April 24th, and the ditch was flooded and overflowing for 
several hours, all the Ranunculus plants being bent downwards towards the south 
when the water had passed over and through them : that the flooding in question 
distributed the spores which caused the sudden and extensive outbreak on May 6th 
to 12th will hardly be questioned after what follows, for I shall show that it requires 
from a fortnight to three weeks to develope a white disease-spot in the leaf from a 
spore germinated on its epidermis. 
