At the left, pure seed of the alfalfa; at the right, alfalfa seed mixed with foreign seed, as it is often found in the market. Alfalfa is a rather difficult crop to start, and it is obviously desirable that pure seed should be used. Once the plant has become well rooted, it will hold its own against all invaders.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 10 Chapter 8