The Book of Alfalfa: History, Cultivation and Merits / Its Uses as a Forage and Fertilizer

by F. D. Coburn

THE CHIEF ADULTERANT

“At present, as stated, Yellow trefoil is the chief adulterant used in American alfalfa seed. A number of cases, indeed, of complete or almost complete substitution of Yellow trefoil for alfalfa seed have come to the writer’s attention within the past year. It is important, therefore, for farmers to know the characteristic marks of distinction between the seed of alfalfa and of its chief adulterants. What are the chief characteristics of alfalfa seed? [Facing page 13] are samples of pure alfalfa seed, photographed under a magnification of five diameters. It will be noted that seeds of three general types exist: (1) A kidney-shaped type, marked ‘a’ in the illustration; (2) a type in which one end terminates in an acute wedge, marked ‘e’; and (3) a type that is round or nearly so, marked ‘b’. These types clearly illustrated, arranged for comparison in parallel rows are [shown] opposite page 44. See also [page 27]. It should be noticed that type 2 is the most characteristic and frequent, and that the perfectly round type is extremely rare. This angular slant toward one tip of the seed is found nowhere among any of the adulterants. Neither does the kidney shape of seed occur, except in Bur clover; and, in that case, the difference in the size of the seeds of the two species is sufficient to distinguish them, in most instances.

Yellow Trefoil: Black Medic: Hop Clover (Medicago lupulina)

“It is when we consider the round or roundish type of alfalfa seed that there is difficulty in distinguishing from alfalfa the seeds of Yellow trefoil and of Sweet clover ([illus.] opp. p. 26), which latter frequently occurs as a weed seed, and possibly in some cases in sufficient quantity to be suspected as an adulterant. By comparison of the seeds of alfalfa with the two adulterants just mentioned, ([p. 26]) the resemblances and differences of the three species will become evident. In general the seeds of Yellow trefoil are shorter and rounder than those of alfalfa, the largest seeds of trefoil measuring 0.0629 inch wide by 0.0897 inch long; whereas the largest alfalfa seeds measure 0.0653 inch wide by 0.1153 inch long; so that the largest alfalfa seeds are a trifle wider and more than a third again as long as the largest trefoil seeds. The smallest seeds of Yellow trefoil are usually plumper and shorter than those of alfalfa (0.0511 inch wide by 0.0291 inch long, as compared with 0.0496 inch wide by 0.0751 inch long in alfalfa); nevertheless, among both the small and the large seeds, so far as the criterion of size goes, individuals occur that equally well belong to either species, and the average differences in size are not so great as the differences found on comparing the largest and the smallest seeds of the two species, the average for the trefoil being 0.0574 inch by 0.0799 inch, and for alfalfa 0.0582 inch by 0.0944 inch. So it will be seen at once that while trefoil seeds as a rule are smaller, shorter and rounder than those of alfalfa, the rule is transgressed by many individuals. We must, therefore, turn to the form and general outline of the seed. A farmer can detect at once an attempt to substitute wholly Yellow trefoil for alfalfa seed by the fact that in no case will the kidney-shaped or the regular-pointed types of seed be found in trefoil, whereas these always occur in alfalfa. ([Illustrated] opp p. 26.)

“In the more common cases, where adulteration rather than complete substitution is practiced, detection is more difficult—is practically impossible, in fact, without the aid of a lens or magnifying glass having a power of about fifteen diameters. There are many seeds of trefoil which can scarcely be distinguished from certain rounded seeds of alfalfa. Generally, however, the trefoil seed has a little projection or “beak” on the middle line of the seed, just back of the scar marking where the seed was attached to the pod. This is rarely found in alfalfa.

“Bur clover as an adulterant is probably not so frequently used as Yellow trefoil, since the larger size of its seed renders detection easy. Were it not for this fact, Bur clover would be a most effective adulterant, because its seeds resemble those of alfalfa more closely than do those of Yellow trefoil. There are, of course, smaller seeds of Bur clover and larger seeds of alfalfa that approximate each other in size, but the average Bur clover seeds measure 0.0604 inch by 0.1188 inch, as compared with an average for alfalfa of only 0.0582 inch by 0.0944 inch.

“So far as the plants of Yellow trefoil and Bur clover are concerned, they are easily distinguishable from alfalfa. Both are of lower growth, as a rule, than alfalfa. Both have wider leaflets, which, in Bur clover, are like broad, inverted wedges. The flowers of these plants are yellow, and are borne in scanty clusters. The pods are wholly unlike those of alfalfa. Alfalfa has a spiral pod of two or three turns ([p. 32]), containing as many as five or six seeds. Yellow trefoil has a straight pod ([p. 32]), containing but one seed. Bur clover has a coiled pod ([p. 33]), but covered with bristly projections that give the plant its name. Where adulteration or substitution is practiced, some of the pods are very apt to occur in the bulk seed, and they can then easily be identified and distinguished from those of alfalfa.

“Seed of Sweet clover seems to occur frequently in western-grown alfalfa seed ([p. 26]). Sweet clover ([illustrated] in this book) grows to a height frequently of from four to six feet, bearing small, white flowers on slender spikes three or four inches long. Unfortunately, and unlike Yellow trefoil and Bur clover, Sweet clover is generally rejected by stock. On this account, it is a plant of no generally established value for hay or as pasture, although, in some instances, it is successfully used. The seeds of Sweet clover are of a golden yellow when ripe; those of alfalfa, trefoil and Bur clover being greenish yellow. The seed coat of Sweet clover seed is covered with minute elevations, while alfalfa seed is smooth. The seeds of Sweet clover ([p. 26]) are rounder and plumper than those of alfalfa, and have a very pronounced groove between the main body of the seed and the ridge which marks the location of the rootlet of the young plant within. It is this ridge that in alfalfa seeds runs off, as a rule, in a marked slant, but which in both trefoil and Sweet clover, especially in the latter, forms a well-rounded curve to the tip of the seed. No pointed or kidney-shaped seeds are ever seen in Sweet clover. (See [illus.] opp. p. 26.)