TRENDS IN SYSTEMATIC BOTANY
59
V. ANATOMY
Anatomical studies of two general types have considerable taxonomic
application—studies of wood anatomy, particularly of the secondary
xylem, and of the vascular arrangements in the inflorescence and in the
flower.
Wood anatomy has become a frequently employed tool to aid in the
solution of taxonomic problems (see bibliography in Metcalfe and
Chalk, 1950; also Tippo, 1946). Like other tools, it needs to be employed in conjunction with other kinds of data to be most significant.
It has supplied critical evidence to the solution of broad evolutionary
problems such as the origin of the angiosperms. In the surviving angiosperms the phylogeny of the tracheary tissues, including the striking
division of labor between vessels, whose function it is to conduct, and
the tracheids and fibers, which support or at times store, is adequately
preserved. This living record shows a high degree of specialization in the
vascular tissues of the herbs, vines, lianas, succulents, aquatics, and
extreme xerophytes as compared to the vesselless, or less modified vesselbearing, xylem of the large woody trees and shrubs. "Such "facts negate
the possibility not only of deriving structurally primitive types of arboreal
dicotyledons from herbaceous ancestors, but also of deriving the monocotyledons from herbaceous dicotyledons, e.g., the Ranunculaceae"
(I. W. Bailey, 1949). On the other hand, Bailey points out that of the
nearly 100 species of living dicotyledons which have a primitive vesselless type of both primary and secondary xylem, all occur within the
order Ranales, as broadly conceived by Engler and Prantl.
Secondary xylem studies also have applications in taxonomy when
made with a view to establishing the relative standing of groups from
the basis of primitive versus specialized status. On the basis of floral
morphology, the "Amentiferae" have been shifted back and forth between relatively low and high positions in the dicotyledons depending
upon the individual worker's interpretation of the evidence as pointing
to a primitive or a derived group. Such authorities as Eichler, Engler,
and Wettstein considered the group primitive; but studies of the floral
anatomy by Eames and a number of his students, and of pollen morphology (which indicates reduction) are supported by wood anatomical
studies by Tippo (1938) and Petersen (1953) to indicate that the group
is rather highly specialized, and much more so than the Ranales.
When data from wood anatomy are applied to family relationships,
conclusions drawn from them must be considered highly suggestive
rather than definitive (Heimsch, 1942). This applies equally well at
the subfamily level. Whereas the higher taxa within the Leguminosae,
59
V. ANATOMY
Anatomical studies of two general types have considerable taxonomic
application—studies of wood anatomy, particularly of the secondary
xylem, and of the vascular arrangements in the inflorescence and in the
flower.
Wood anatomy has become a frequently employed tool to aid in the
solution of taxonomic problems (see bibliography in Metcalfe and
Chalk, 1950; also Tippo, 1946). Like other tools, it needs to be employed in conjunction with other kinds of data to be most significant.
It has supplied critical evidence to the solution of broad evolutionary
problems such as the origin of the angiosperms. In the surviving angiosperms the phylogeny of the tracheary tissues, including the striking
division of labor between vessels, whose function it is to conduct, and
the tracheids and fibers, which support or at times store, is adequately
preserved. This living record shows a high degree of specialization in the
vascular tissues of the herbs, vines, lianas, succulents, aquatics, and
extreme xerophytes as compared to the vesselless, or less modified vesselbearing, xylem of the large woody trees and shrubs. "Such "facts negate
the possibility not only of deriving structurally primitive types of arboreal
dicotyledons from herbaceous ancestors, but also of deriving the monocotyledons from herbaceous dicotyledons, e.g., the Ranunculaceae"
(I. W. Bailey, 1949). On the other hand, Bailey points out that of the
nearly 100 species of living dicotyledons which have a primitive vesselless type of both primary and secondary xylem, all occur within the
order Ranales, as broadly conceived by Engler and Prantl.
Secondary xylem studies also have applications in taxonomy when
made with a view to establishing the relative standing of groups from
the basis of primitive versus specialized status. On the basis of floral
morphology, the "Amentiferae" have been shifted back and forth between relatively low and high positions in the dicotyledons depending
upon the individual worker's interpretation of the evidence as pointing
to a primitive or a derived group. Such authorities as Eichler, Engler,
and Wettstein considered the group primitive; but studies of the floral
anatomy by Eames and a number of his students, and of pollen morphology (which indicates reduction) are supported by wood anatomical
studies by Tippo (1938) and Petersen (1953) to indicate that the group
is rather highly specialized, and much more so than the Ranales.
When data from wood anatomy are applied to family relationships,
conclusions drawn from them must be considered highly suggestive
rather than definitive (Heimsch, 1942). This applies equally well at
the subfamily level. Whereas the higher taxa within the Leguminosae,