TRENDS IN SYSTEMATIC BOTANY
83
long to the same comparium, a term proposed by Danser (1929). The
experimentalist, of course, is unable to work beyond the limits of the
comparium, as genetic evidence of any sort is here denied him.
The cenospecies of the experimental taxonomist is sometimes the
equivalent of the species, sometimes of the genus. In large genera it
is frequently the counterpart of the subgenus or section. It is quite impossible to make the term commensurate with one taxon or another
of the taxonomist all the time, as its genetically determined basis of
sterility barriers is not absolutely related to the morphological basis of
the taxonomist. In some cases the correlation between the prominent
taxonomic characters and the genetic barriers is very close, but there
are many exceptions.
The terms genus, species, subspecies, variety, and so on have a definite
meaning to the taxonomist, even though these terms cannot be described
with such precision that all workers would classify the same data in the
same way. Likewise, the terms comparium, cenospecies, ecospecies, and
ecotype convey rather precise meanings to the experimental taxonomist.
Plants may be grouped under either classification, but the groupings will
differ somewhat in size and composition depending on which classification is employed. It is undesirable to incorporate the classification of the
experimentalist into the system of the taxonomist, for it would often result
in naming groups that could not properly be distinguished by ordinary
taxonomic methods. If a classification should have to depend upon the
results of experiments in an experiment garden, it would prove to be
intolerably cumbersome and would be summarily rejected. On the other
hand, the terms of, the experimentalist define units that are of more use
to the evolutionist than the genus and species of the taxonomist. These
units of the experimentalist are the natural evolutionary units, and when
they have been worked out by experiment and can be applied in orthodox taxonomy, the resultant classification is a natural one.
XV. THE GENUS LAYIA
For over a dozen years the team of experimental taxonomists at the
Division of Plant Biology of the Carnegie Institution of Washington on
the Stanford University campus grew hundreds of thousands of plants
and performed hundreds of crossing experiments on members of the
Composite subtribe Madiinae (Heliantheae). This subtribe contains
some 85 species, most of which are endemic to California. They are
largely plants of valley floors that do not segregate altitudinal or climatic
ecotypes. They do show much genetic variation and active speciation.
Polyploidy is rare, but otherwise they exhibit many cytological evolu-
83
long to the same comparium, a term proposed by Danser (1929). The
experimentalist, of course, is unable to work beyond the limits of the
comparium, as genetic evidence of any sort is here denied him.
The cenospecies of the experimental taxonomist is sometimes the
equivalent of the species, sometimes of the genus. In large genera it
is frequently the counterpart of the subgenus or section. It is quite impossible to make the term commensurate with one taxon or another
of the taxonomist all the time, as its genetically determined basis of
sterility barriers is not absolutely related to the morphological basis of
the taxonomist. In some cases the correlation between the prominent
taxonomic characters and the genetic barriers is very close, but there
are many exceptions.
The terms genus, species, subspecies, variety, and so on have a definite
meaning to the taxonomist, even though these terms cannot be described
with such precision that all workers would classify the same data in the
same way. Likewise, the terms comparium, cenospecies, ecospecies, and
ecotype convey rather precise meanings to the experimental taxonomist.
Plants may be grouped under either classification, but the groupings will
differ somewhat in size and composition depending on which classification is employed. It is undesirable to incorporate the classification of the
experimentalist into the system of the taxonomist, for it would often result
in naming groups that could not properly be distinguished by ordinary
taxonomic methods. If a classification should have to depend upon the
results of experiments in an experiment garden, it would prove to be
intolerably cumbersome and would be summarily rejected. On the other
hand, the terms of, the experimentalist define units that are of more use
to the evolutionist than the genus and species of the taxonomist. These
units of the experimentalist are the natural evolutionary units, and when
they have been worked out by experiment and can be applied in orthodox taxonomy, the resultant classification is a natural one.
XV. THE GENUS LAYIA
For over a dozen years the team of experimental taxonomists at the
Division of Plant Biology of the Carnegie Institution of Washington on
the Stanford University campus grew hundreds of thousands of plants
and performed hundreds of crossing experiments on members of the
Composite subtribe Madiinae (Heliantheae). This subtribe contains
some 85 species, most of which are endemic to California. They are
largely plants of valley floors that do not segregate altitudinal or climatic
ecotypes. They do show much genetic variation and active speciation.
Polyploidy is rare, but otherwise they exhibit many cytological evolu-