Some Cactus Seedlings-1
From this print it will be seen that Mr. Burbank first plants his seedlings closely in a shallow box. These boxes or "flats" are about eighteen inches square and two or three inches in height. No two of the seedlings, of course, are exactly alike, and from these Mr. Burbank makes his first selection. The box or "flat" at the right contains one hundred cactus seedlings; the "flat" at the left contains four hundred.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 1 Chapter 6