De Agricultura
Philo Judaeus
The works of Philo Judaeus, the contemporary of Josephus, volume 1. Yonge, C. D., translator. London: Henry G. Bohn, 1854.
At all events, men say, that the ancients compared the principles of philosophy, as being threefold, to a field; likening natural philosophy to trees and plants, and moral philosophy to fruits, for the sake of which the plants are planted; and logical philosophy to the hedge or fence: