The researches of Tisserand may be summed up as follows:
| Year. | Population in millions | Acres under wheat | Average crop in bushels per acre | bushels |
|---|---|---|---|---|
| 1789 | 27.0 | 9,884,000 | 9 | 87,980,000 |
| 1831-41 | 33.4 | 13,224,000 | 15 | 194,225,000 |
| 1882-88 | 38.2 | 17,198,000 | 18 | 311,619,000 |