[12] In order to meet this difficulty we must recognize two sorts of
species. The systematic species are the practical units of the
systematists and florists, and all friends of wild nature should do
their utmost to preserve them as Linnaeus has proposed them. These units
however, are not really existing entities; they have as little claim to
be regarded as such as genera and families. The real units are the
elementary species; their limits often apparently overlap and can only
in rare cases be determined on the sole ground of field observations.
Pedigree-culture is the method required and any form which remains
constant and distinct from its allies in the garden is to be considered
as an elementary species.
In the following lectures we shall consider this point at length, to
show the compound nature of systematic species in wild and in cultivated
plants. In both cases, the principle is becoming of great importance,
and many papers published recently indicate its almost universal
acceptation.
Among the systematic subdivisions of species, not all have the same
claim to the title of elementary species. In the first place the cases
in which the differences may occur between parts of the same individual
are to be excluded. Dividing an alpine plant into two halves and [13]
planting one in a garden, varietal differences at once arise and are
often designated in systematic works under different varietal names.
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