Field Observations on Development of Potato Blight 189 
in explanation of the rapid onset of epidemics of potato 
blight, but without any evidence more critical than has hitherto 
been brought forward in his other papers on mycoplasm ; it is 
obvious that the possibility of explaining the propagation of potato 
blight from year to year by the agency of mycoplasm will stand or 
fall by the mycoplasm theory in general, which, it may be said, is 
still entirely unproven. 
Nearly all the work on the means of over-wintering of potato 
blight referred to above, has been done on a small scale under 
experimental conditions, and few careful observations have been 
made in the field as to the way in which the fungus first develops 
in potato fields planted under ordinary conditions. On account of 
the uncertainty still existing as to the means by which the earliest 
appearance of blight in epidemic form in the growing crop is 
brought about, Dr. A. S. Horne and the writer decided to carry out 
observations in certain parts of the country with a view to throwing 
further light on this matter, if possible. It was clear that the dis¬ 
tricts chosen for these observations should be areas in which the 
fungus develops in epidemic form, as it were endemically, i.e., with¬ 
out infection by spores brought by air currents from other quarters. 
Consideration of the progress of the epidemic of potato blight in 
1917 shewed that the Penzance district and the Isle of Wight 
fulfilled this requirement, for in that year Phytophtliora developed 
in both these areas before it appeared in the adjacent parts* 
Although the observations around Penzance were the first to be 
taken, those made in the Isle of Wight will first be described, as 
operations there were conducted in greater detail and with better 
facilities. In the original program, it was arranged that the writer 
should make observations in the Penzance district, and that Dr. 
Horne shoulddo the same in the Isle of Wight, hutafter making some 
preliminary visits to the island, the latter was unfortunatly preven¬ 
ted by illness from continuing the work, the direction of which 
then devolved upon Professor F. W. Oliver and the writer. 
Observations in the Isle of Wight. 
Through the financial asistance of the Food Production De¬ 
partment, and the kind interest of Mr. Lawrence Weaver, C.B.E. 
(Food Production Department) and of Professor F.W. Oliver, F.R.S., 
certain members of the staff and students of University 
College, London, including Misses E. Goodyear, E. A. Fraser, 
M. L. Hett, M. Munro, E.J. Whitehead, B. Russell Wells, M. A, 
Sutton, H. S. Pearson, H. A. Bond, A. Gotlieb, together with Mr. 
H. Stansfield of the Imperial College, and Miss Osborn and Miss 
Barker of Bedford College, spent several weeks in the island during 
