A number of different strains of white sweet clover are to be found in
the average field, but most of them are not as marked or as conspicuous
as the different strains of red clover. The principal differences
between strains of sweet clover are in leafiness, habit of growth, and
date of blooming.
[Illustration: Fig. 4.--Buds produced on the crown of a sweet-clover
plant at the end of the first season's growth. These buds will produce
the first crop the second season.]
Occasional plants are especially heavy seed producers and bear many
pods containing more than one seed. Other plants bloom earlier than
the average date for white sweet clover, and it may be possible by
selecting such strains to find one which matures early enough to
produce two crops a season at high altitudes in the northern sections
of the United States.
Fields of an exceptionally early blooming strain were found in
Illinois, Iowa, and North Dakota in the summer of 1916. The plants
were different in type of growth from the ordinary white sweet clover,
being most conspicuous from the fact that they were in bloom during
the first week of June, which is at least three weeks earlier than the
ordinary species should bloom in these localities.
[Illustration: Fig. 5.--Root of white sweet clover (on the left)
and of biennial yellow sweet clover (on the right). These roots were
collected on October 28, 1915, at Arlington, Va., from adjacent plats
seeded to cuts and sweet clover on April 10, 1915. Note the difference
in the size of the roots. Tubercles are present on the right-hand side
of each root.]
An annual white-flowered sweet clover was found in several localities
in the fall of 1916. The seed which produced these plants was grown
in Alabama. These plants resembled _Melilotus alba_ in most respects
except that they were strictly annual. They flowered and matured
seed abundantly in South Dakota and North Dakota. It has not been
determined whether this is a distinct species or merely an annual
strain of the species mentioned.