A
wide distance between the homes of two doubtful forms leads many
naturalists to rank both as distinct species; but what distance, it
has been well asked, will suffice? if that between America and Europe
is ample, will that between the Continent and the Azores, or Madeira,
or the Canaries, or Ireland, be sufficient? It must be admitted that
many forms, considered by highly-competent judges as varieties, have
so perfectly the character of species that they are ranked by other
highly-competent judges as good and true species. But to discuss
whether they are rightly called species or varieties, before any
definition of these terms has been generally accepted, is vainly to
beat the air.
Many of the cases of strongly-marked varieties or doubtful species
well deserve consideration; for several interesting lines of argument,
from geographical distribution, analogical variation, hybridism, etc.,
have been brought to bear on the attempt to determine their rank. I
will here give only a single instance,--the well-known one of the
primrose and cowslip, or Primula veris and elatior. These plants
differ considerably in appearance; they have a different flavour and
emit a different odour; they flower at slightly different periods;
they grow in somewhat different stations; they ascend mountains to
different heights; they have different geographical ranges; and
lastly, according to very numerous experiments made during several
years by that most careful observer Gartner, they can be crossed only
with much difficulty.
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