64
DAVID D. KECK
value (Towers and Gibbs, 1953). Many such tests have been tried by
Gibbs, who also has recently reviewed the subject (1945, 1954).
A prolonged series of investigations on the chemical compounds of
which turpentine is composed have led to interesting taxonomic conclusions in the genus Finns (Mirov, 1953). Each species of pine possesses an individually characteristic turpentine. This turpentine is constant for the species over the whole of its range, so far as tested. The
specificity of these chemical compounds in the Coniferae makes them of
considerable taxonomic significance at the generic, specific, and even
subspecific levels.
XII. CYTOGENETICS
This branch of biology is the vigorous hybrid between two fields,
themselves relatively new, cytology and genetics. Much attention has
been attracted to this discipline, which is among the foremost of those
which undertake to unravel the mysteries of organic evolution. This it
does through the application of genetic principles operating under
known sets of conditions. The interplay of heredity and environment,
as these influence the development, migration, and change of the organism, is studied, and the laws governing phylogenetic progression are
worked out. Speciation is a prime concern of the cytogeneticist, and his
delight is to recapitulate experimentally the origin of a species or other
taxon. Obviously the activities of the cytogeneticist are of primary
concern to the taxonomist, for much of the data for an improved classification are being gathered by him, and new methods and ideas are
constantly coming to light in his field.
The approaches of the cytogeneticist are varied, and the next sections
of cytology and genetics will indicate some of the ramifications of importance to the taxonomist.
XIII. CYTOLOGY
The contributions made to taxonomy by the field of cytology have
come almost exclusively from the nucleus rather than from the cytoplasm of the cell. Cytology has contributed chromosome number,
morphology, and behavior as an important source of characters, and
papers on the cytotaxonomy of this or that group have become abundant.
Chromosome number is an important taxonomic character because as
a general rule all the members of a species have the same number. Even
in some genera having many species no deviation in the chromosome
number has been found in the whole genus, although this is not general.
Exceptions to the rule occur even on the species level, however, par-
DAVID D. KECK
value (Towers and Gibbs, 1953). Many such tests have been tried by
Gibbs, who also has recently reviewed the subject (1945, 1954).
A prolonged series of investigations on the chemical compounds of
which turpentine is composed have led to interesting taxonomic conclusions in the genus Finns (Mirov, 1953). Each species of pine possesses an individually characteristic turpentine. This turpentine is constant for the species over the whole of its range, so far as tested. The
specificity of these chemical compounds in the Coniferae makes them of
considerable taxonomic significance at the generic, specific, and even
subspecific levels.
XII. CYTOGENETICS
This branch of biology is the vigorous hybrid between two fields,
themselves relatively new, cytology and genetics. Much attention has
been attracted to this discipline, which is among the foremost of those
which undertake to unravel the mysteries of organic evolution. This it
does through the application of genetic principles operating under
known sets of conditions. The interplay of heredity and environment,
as these influence the development, migration, and change of the organism, is studied, and the laws governing phylogenetic progression are
worked out. Speciation is a prime concern of the cytogeneticist, and his
delight is to recapitulate experimentally the origin of a species or other
taxon. Obviously the activities of the cytogeneticist are of primary
concern to the taxonomist, for much of the data for an improved classification are being gathered by him, and new methods and ideas are
constantly coming to light in his field.
The approaches of the cytogeneticist are varied, and the next sections
of cytology and genetics will indicate some of the ramifications of importance to the taxonomist.
XIII. CYTOLOGY
The contributions made to taxonomy by the field of cytology have
come almost exclusively from the nucleus rather than from the cytoplasm of the cell. Cytology has contributed chromosome number,
morphology, and behavior as an important source of characters, and
papers on the cytotaxonomy of this or that group have become abundant.
Chromosome number is an important taxonomic character because as
a general rule all the members of a species have the same number. Even
in some genera having many species no deviation in the chromosome
number has been found in the whole genus, although this is not general.
Exceptions to the rule occur even on the species level, however, par-