F. T. Brooks. 187 
AN ACCOUNT OF SOME FIELD OBSERVATIONS ON 
THE DEVELOPMENT OF POTATO BLIGHT. 
By F. T. Brooks, M.A. 
[With Two Figures in the Text] 
Introduction. 
E VER since the fungus Phytophthora infestans first became the 
subject of scientific investigation, there has been a good deal 
of obscurity as to the way in which it is carried over from year to 
year. The conidia are short-lived and therefore do not serve to 
tide the fungus over the winter. 
In spite of prolonged search, de Bary 1 failed to find resting 
oospores in diseased potato plants, the fungus in this respect being 
unlike many other species of Phytophthora. He was of the opinion, 
therefore, that potato blight was carried over from year to year by 
means of mycelium hibernating in partly diseased tubers, and he 
obtained definite evidence that mycelium of this kind sometimes 
passed from the tubers into young shoots, on which the fungus 
developed its spores above ground, thus forming starting points for 
an epidemic. 
In 1875, Worthington Smith 3 reported the discovery of 
resting oospores of the blight fungus in tissues of diseased potato 
plants, but the evidence was not conclusive and, in the absence of 
confirmation by other observers, there has always been doubt whether 
these bodies really belonged to Phytophthora infestans. 
With the discovery in America by Jones 3 and Clinton 4 that 
Phytophthora infestans developed oospores in pure culture, attention 
was again directed to the possibility of infection arising from such 
resting bodies during the early summer, and Pethybridge® followed 
up this line of enquiry in Ireland, Although he confirmed the 
development of oospores in culture, he failed to find them in dis¬ 
eased plants. In connection with this work, Pethybridge put to the 
test the view that the fungus is carried over the winter by my 
celium in partly diseased tubers, and, obtained some experimental 
evidence that, when planted in pots chiefly under greenhouse 
conditions, a very small percentage of blighted tubers functioned in 
this way, the great majority either giving rise to perfectly healthy 
1 de Bary, A. Researches into the nature of the potato-fungus— 
Phytophthora in/estans. Journ. Roy. Agric. Soc. England, 1876, pp. 239-269. 
3 Smith, \V. G. The resting spores of the potato disease. Gardeners 
Chronicle, 1875, p. 35. 
* Jones, E.R. Resting spores of the potato fungus. Science, 1909, p, 813. 
* Clinton, G. P. Oospores of potato blight. Conn. Agric. Exp. Stat. 
Rept. 1909-10, p. 753. 
‘ Pethybridge, G. H. Investigations on potato diseases. 5th., 6th., 7th., 
Reports, 1914-6. Journ. Irish Bd. Agric. 
