In other instances the groups of
elementary forms as they are shown by direct observation, have been
adjudged by many authors [52] to be too large to constitute species.
Hence the polymorphous genera, concerning the systematic subdivisions of
which hardly two authors agree. Brambles and roses are widely known
instances, but oaks, elms, apples, and pears, _Mentha_, _Prunu_s,
_Vitis_, _Lactuca_, _Cucumis_, _Cucurbita_ and numerous others are in
the same condition.
In some instances the existence of elementary species is so obvious,
that they have been described by taxonomists as systematic varieties or
even as good species. The primroses afford a widely known example.
Linnaeus called them _Primula veris_, and recognized three types as
pertaining to this species, but Jacquin and others have elevated these
subspecies to the full rank of species. They now bear the names of
_Primula elatior_ with larger, _P. officinalis_ with smaller flowers,
and _P. acaulis_. In the last named the common flower-stalk is lacking
and the flowers of the umbel seem to be borne in the arils of the basal
leaves.
In other genera such nearly allied species are more or less universally
recognized. _Galium Mollugo_ has been divided into _G. elatum_ with a
long and weak stem, and _G. erectum_ with shorter and erect stems;
_Cochlearia danica_, _anglica_ and _officinalis_ are so nearly allied as
to be hardly distinguishable.
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