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showed constancy were retained, while those of low stability
were discarded.

Two broad groups of the entities may be recognized. For
present purposes, these are designated "convariants" in accord
with proposals for an international code for cultivated plants.
"Convariant" is used at the same level of classification of cul-
tivated plants as "subspecies" is used for wild ones. It does
not carry any suggestion of geographic separation, for obvious
reasons, as does subspecies for native populations.

The characteristics which differentiate the two convariants
are: Group A: silver-colored stem, and light tan, smooth-
surfaced roots. Group B: brown to yellow stems, and dark brown,
rough-surfaced roots. These are well-defined groups, with very
little over-lapping. The genetic systems governing this sta-
bility is unknown, but whether one or many genes are involved is
not significant taxonomically, because these characteristics pro-
vide a convenient method for distinguishing groups of closely re-
lated plants.

The establishment of the two categories (convariants) solves
one problem, but introduces several others. Upon examination of
plants from categories A and B, one finds that characters, other
than those used for the major division, cross back and forth be-
tween the convariants. For example, the branching pattern of
the variants is a significant taxonomic character. In both con-
variant A and convariant B may be found plants with unbranched,
tall stems, or stems branched once, twice, three, four, or five
times. The same may be said for the numbers and shapes of the
lobes of the leaf, for the coloration of the young foliage, the
petioles, etc.