Sentence:  Having for many years considered oil as the great <WSD>pabulum</WSD> of plants, I was much hurt by the result of some experiments, which state oil as "poison"; and turning this in my thoughts a thousand times over, it at last occurred to me, that though oil, as oil in its "crude" state, might act as a poison, yet it might be so changed as to convey it with great advantage to the soil, ... 
Meaning of the word marked with <WSD> tags:  Food or fodder, particularly that taken in by plants or animals.