FORTY YEARS O F QENECOLOQY
177
sectifolim, the former characteristic of fen communities and shallow
depressions in grassland areas subject to intermittent flooding and the
latter of wet grassland, was less than Q m in width; the two forms were
entirely restricted to their characteristic habitats, and hybrids were
encountered only in the ecotone. Reciprocal transplant experiments
were carried out with these two forms; millani showed only moderate
growth in the dissectifdim habitat, and dissectifolius failed altogether to
survive in the millani habitat.
Briggs considers that the identity of the different races is maintained
by their ecological specialization, which is sufliciently strong to ensure
that hybrid derivatives have no chance of success in the wild except in
ecotones, which tend in general to be narrow. This seems to be true also
of several taxonomic “species pairs” in the European flora such as
Silene maritima and S. vulgaris, Melandrium rubrum and M . album, and
Geum rivale and G: urbanum. The common features here are that the
entities concerned in each pair are distinguished from each other by
several consistent differentiae : they are freely interfertile in experimental crossings, they have distinct ecological tolerances, and they do
not hybridize freely in the wild except where ecotones occur or where
there has been habitat disturbance. In addition, the total geographical
ranges although overlapping are not coincident, and with some there is
evidence that the distinctness has persisted since early post-glacial
times (Turrill, 1946).
Obviously all of the examples quoted so far are interpretable as cases
where two or more races have differentiated allopatrically in both
morphological and physiological properties, and have then acquired
sympatric ranges by migration, their integrity being preserved subsequently in the common area by strong ecological specialization. There
are several essentially similar cases where ecological races have been
given taxonomic recognition as subspecies because the differentiae are
fewer, or less distinctive, than would normally be required of taxonomio
species. The subspecies of Dactylorchis incurnata in the British Isles
constitute habitat races showing morphological differentiation principally in floral characteristics (Heslop-Harrison, 1953a, 1956). The
differentiae are maintained in cultivation, and are associated with
phenological and other physiological differences. Populations referable
to the various subspecies often occur in close proximity without loss of
identity, and occasionally even intermingled where there are rapid
alternations in habitat. Thus in one locality plants referable to pulchella
and coccinea occurred together in a field traversed by an old herringbone drainage system. The hollows of this carried a wet-soil vegetation
forming a continuation of a lake-side fen. On the drier mineral soil of the
ridges, 85% of the plants were coccinea; in the hollows, 96% were
177
sectifolim, the former characteristic of fen communities and shallow
depressions in grassland areas subject to intermittent flooding and the
latter of wet grassland, was less than Q m in width; the two forms were
entirely restricted to their characteristic habitats, and hybrids were
encountered only in the ecotone. Reciprocal transplant experiments
were carried out with these two forms; millani showed only moderate
growth in the dissectifdim habitat, and dissectifolius failed altogether to
survive in the millani habitat.
Briggs considers that the identity of the different races is maintained
by their ecological specialization, which is sufliciently strong to ensure
that hybrid derivatives have no chance of success in the wild except in
ecotones, which tend in general to be narrow. This seems to be true also
of several taxonomic “species pairs” in the European flora such as
Silene maritima and S. vulgaris, Melandrium rubrum and M . album, and
Geum rivale and G: urbanum. The common features here are that the
entities concerned in each pair are distinguished from each other by
several consistent differentiae : they are freely interfertile in experimental crossings, they have distinct ecological tolerances, and they do
not hybridize freely in the wild except where ecotones occur or where
there has been habitat disturbance. In addition, the total geographical
ranges although overlapping are not coincident, and with some there is
evidence that the distinctness has persisted since early post-glacial
times (Turrill, 1946).
Obviously all of the examples quoted so far are interpretable as cases
where two or more races have differentiated allopatrically in both
morphological and physiological properties, and have then acquired
sympatric ranges by migration, their integrity being preserved subsequently in the common area by strong ecological specialization. There
are several essentially similar cases where ecological races have been
given taxonomic recognition as subspecies because the differentiae are
fewer, or less distinctive, than would normally be required of taxonomio
species. The subspecies of Dactylorchis incurnata in the British Isles
constitute habitat races showing morphological differentiation principally in floral characteristics (Heslop-Harrison, 1953a, 1956). The
differentiae are maintained in cultivation, and are associated with
phenological and other physiological differences. Populations referable
to the various subspecies often occur in close proximity without loss of
identity, and occasionally even intermingled where there are rapid
alternations in habitat. Thus in one locality plants referable to pulchella
and coccinea occurred together in a field traversed by an old herringbone drainage system. The hollows of this carried a wet-soil vegetation
forming a continuation of a lake-side fen. On the drier mineral soil of the
ridges, 85% of the plants were coccinea; in the hollows, 96% were