"The Coming Race", Chapter XXIII, by Edward Bulwer-Lytton

Why does he compare corn to wheat? Because corn is a much older word than 1492. Historically, before the Europeans discovered the New World, 'corn' was a word for any type of cereal grass crop, such as wheat. Hence you find translations of the Bible using the word 'corn', not to describe New World maize, but various old world grains.

esculent: fit to be eaten; edible

The picture used is of an old underground mushroom cellar, where common mushrooms are cultivated in beds. By Édouard Bergé, used here under the Creative Commons Attribution 3.0 Unported license (https://creativecommons.org/licenses/by/3.0/deed.en).

It's really hard to find pictures of underground/cavern farms or livestock herding, it just isn't done. For pretty obvious reasons. I mean, there are a tiny handful of examples using various artificial lighting, but the pictures of it look more like labs than caves or even farms, so not very suitable for our purpose here.

To follow along: https://www.gutenberg.org/files/1951/1951-h/1951-h.htm#link2HCH0023