Pursuing this theory it seems likely that the solanin of the potato is its natural protection against the disease caused by the fungus phytophthora infestans.
"Grain and Chaff from an English Manor"
Arthur H. Savory
The now well-known spots, at first pale and then brown and fringed with a whitish mould-like growth-the conidiophores of the phytophthora-were observed during the dull cloudy and wet weather, cooler than usual, when the atmosphere was saturated for days together, in July and August.
"Disease in Plants"
H. Marshall Ward
We must remember that prior to 1860 the life-history of phytophthora was not known.
"Disease in Plants"
H. Marshall Ward