200 
F. T. Brooks. 
variety growing partly under trees about fifty yards away. By this 
date nearly all early varieties had been dug in this district. 
Numbers of other potato areas were examined in the vicinity 
of Penzance at this time with negative results, and it is noteworthy 
that up to June 23rd not a trace of blight was found on varieties 
of potatoes other than earlies and second-earlies. The weather 
remained dry until about the middle of July and there was no 
appreciable development of blight on main crop potatoes in the west¬ 
ern parts of Cornwall until the end of that month. Of course had wet 
intervened when the early varieties were first affected the disease 
would have spread with its usual rapidity. 
Conclusions. 
The observations taken in the Penzance district agree in 
kind with those made in the Isle of Wight and shew with- the latter 
that the earliest outbreaks of blight developing in situ are of strictly 
limited extent and that from them the fungus develops centrifugally 
under favourable conditions until the spores are so widely 
distributed in the air that infection of susceptible plants becomes 
universal. The observation that blight affects the tubers at a very 
early stage in the development of the disease is noteworthy, as is 
also the evidence presented that these do not generally become 
infected from the main stem via the stolons. The facts observed 
are capable of interpretation either by infection from the soil 
through the agency of some form of resting body or by infection 
from blighted shoots growing upwards from diseased sets. The 
latter were not found in spite of careful search, although it is 
known that they have occasionally functioned under experimental 
conditions. The fact that the first plants to be affected are in 
limited groups may at first thought appear to invalidate the 
possibility of infection from the soil, but it does not follow that 
resting bodies, if formed, would be regularly distributed in the soil 
and it is likely that only a few would function and be successful in 
causing blight to develop on the plants. One is reluctant to give 
up the idea of some form of resting body in the life-history of this 
fungus in nature, for it would be suprising if this fungus, which can 
produce oospores in artificial culture, were unable to form these 
in nature under certain, at present unknown, conditions. 
These observations shew that it will be a matter of difficulty, 
and perhaps also of considerable luck, to obtain critical evidence as 
to the mode in which the blight fungus is carried over from year to 
year in crops of potatoes grown under ordinary conditions. In 
shewing that the first attacks are strictly limited where extraneous 
infection is not operative, the solution of the problem is advanced 
slightly, and by continued attack along these and other lines the 
obscurity which still exists in regard to the life-history of Phyto- 
phthora infestans in the field should be removed. 
In conclusion, the grateful thanks of the observers and the 
writer are due to all those in the Isle of Wight and in the Penzance 
district who provided facilities for carrying out these observations, 
especially to Mr. C. Martin, Instructor in Horticulture for the Isle 
of Wight, and also to Professor Oliver, F.R.S.for his great interest 
and help throughout the work in the Isle of Wight. 
