The leaf-like appendages put forth from a germinating plant when it first comes from the ground are called cotyledons. The entire coteries of higher plants are divided into two great classes, accordingly as their germinating stalks put forth one or two cotyledons. All the plants with which one deals in the garden are di-cotyledons, like those here shown. The cotyledons are uniformly smooth in contour (Mr. Burbank has seen but a single exception to this in his entire experience), and they serve as a reserve supply of food while the young leaves are getting under way.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 7 Chapter 1