Chapter II: The Wheat Problem, by Sir W. Crookes. (John Murray, 1899.)

The Production of Wheat in the British Empire, by A. E.
Humphries. (_Journal of the Royal Society of Arts_, Vol.
LVII, p. 229.)

Wheat Growing in Canada, the United States, and the Argentine,
by W. P. Rutter. (Adam and Charles Black, 1911.)

Agricultural Note-Book, by Primrose McConnell. (Crosby,
Lockwood and Son, 1910.)