Abstracts of Papers - Harvard Forest - Harvard University

Australian National University, Canberra, A.C.T.
2601. - Differing ontogenetic origin of PCR
("Kranz") sheaths in leaf blades of C, grasses
(Poaceae)
The origin and development of ground meristem and
provascular tissue have been examined in leaf blades
of eight C4 grasses, representing different taxonomic
groups and the three recognized biochemical C4 types
(NADP-ME, NAD-ME and PCK types). Comparisons were
made with the C3 species, Festuca arundinacea (pooid).
In NAD-ME (Panicum effusum, eupanicoid; Eleusine
coracana, chloridoid) and PCK (Sporobolus elongatus,
chloridoid) species, the provascular tissue of
primary veins gives rise to xylem, phloem and a
mestome sheath; associated ground meristem differ-
entiates as PCA ("C4 mesophyll") and the PCR ("Kranz")
sheath. This parallels development in the C3 grass,
except that associated ground meristem differentiates
into mesophyll and a parenchymatous bundle sheath.
By contrast, the provascular tissue of NADP-ME C4
species (Panicum bulbosum and Digitaria brownii, eu-
panicoid; Cymbopogon exaltatus, andropogonoid)
differentiates into xylem, phloem and a PCR sheath;
associated ground meristem giving rise only to PCA
tissue. Findings support W.V. Brown's hypothesis
that the PCR sheaths of NAD-ME and PCK-type C4 grasses
are homologous with the parenchymatous bundle sheaths
of C grasses, whereas in NAD-ME C4 grasses, they are
homologous with mestome sheaths. Aristida
biglandulosa and Arundinella nepalensis have unusual
C4leaf anatomy of special interest to this hypo-
thesis.
DERSTINE, KITTIE S.* and SHIRLEY C. TUCKER.
Department of Botany, Louisiana State University,
Baton Rouge, LA 70803
-Comparative floral ontogeny of Parkinsonia
aculeata (Caesalpinioideae), Lupinus havardii
(Papilionoideae) and Acacia baileyana (Mimos-
oideae).
The three subfamilies of Fabaceae are distinguished
on the basis of floral symmetry, aestivation of
petals in bud (valvate or imbricate), degree of
fusion in calyx and corolla, and morphology of seeds
and leaves. The first three characteristics will be
addressed, using SEM primarily. Ontogenetic studies
of a representative taxon in each subfamily are
intended to determine when during development these
diagnostic features first become evident. In each
taxon, order of initiation of sepals and petals is
used to establish first evidence of symmetry. Middle
developmental stages elucidate first indications of
aestivation and/or apparent fusion among sepals,
petals and filaments. Final flower form is seen in
later developmental stages with petal expansion into
divergent forms and cell differentiation as well as
degree of filament fusion and further apparant petal
fusion.
DICKISON, WILLIAM C. Department of Biology,
University of North Carolina, Chapel Hill, NC
27514. - Fruits and seeds of the Cunoniaceae.
Cunoniaceae fruit morphology varies from ventrally
dehiscent follicles, and dry, septicidally dehiscent
capsules, to dry, indehiscent capsules, fleshy
drupes, berries, and winged fruit types. The fol-
licular fruit is the primitive condition in the
family from which dehiscent capsules and indehiscent
forms evolved. The majority of species produce
fruit in which the pericarp is differentiated into
exocarp, mesocarp, and lignified, fibrous endocarp.
Developmental and Structural Section 19
Major shifts ih dispersal strategy resulted in more
advanced taxa in which the entire fruit is modified
for seed dispersal and protection. Most dehiscent-
fruited genera produce seeds with dispersal append-
ages in the form of wings or hairs. Hairs are
generally apically comate, less commonly distributed
in other patterns. Genera with indehiscent fruits
possess a variety of seed morphologies but all are
devoid of wings or hairs. Seed coats are exotegmic
in construction, that is, the outer epidermis of
the inner integument differentiates into the
mechanical layer. Two distinct trends are recog-
nized in seed coat structure: (1) reduction in seed
coat thickness, including loss of a mechanical layer,
and (2) amplification of the seed coat by secondary
divisions of integumentary cells in the post-
fertilization ovule. The diversity of seed surface
patterns will be described and illustrated.
DIGGLE, PAMELA K.* and DARLEEN A. DEMASON. Botany
and Plant Sciences, University
Riverside, 92521. - Developmental
of California,
relationship
between the PTM and the STM in Yucca whipplei.
Histological and anatomical observations were made
on plants ranging from embryos to three-year-old
plants of Yucca whipplei Torr. var. percursa Haines.
Our objective was to determine the time and position
of origin, ontogenetic relationship, and function
of the primary thickening meristem (PTM) and the
secondary thickening meristem (STM) during development
of the vegetative axis. The PTM arises in
the stem periphery during germination. It is longitudinally
continuous from beneath the youngest
leaf primordia to the primary root, and functions
in the production of primary vascular bundles and
ground tissue. The STM arises ontogenetically from
the PTM in the base of two- to three-month seedlings
and produces secondary vascular bundles and ground
tissue. Parenchyma in the ground tissue is arranged
in anticlinal cell files continuous from beneath the
leaf bases, through the cortex and central cylinder
to the pith. Individual vascular bundles in the
primary body are collateral. The parenchyma cells
of the ground tissue of the secondary body are also
arranged in files continuous with those of the primary
parenchyma. Secondary vascular bundles are
amphivasal and have an undulating path with frequent
anastomoses. The PTM and STM, primary and secondary
vascular bundles, and files of primary and secondary
ground tissue are continuous at all developmental
stages studied. Development of the primary body is
histologically and quantitatively similar to development
in monocotyledons which possess only a PTI;
and secondary growth is interpreted as a developmental
continuation of the process of primary thickening.
DUTE, ROLAND
R. Department of Botany, Plant
Pathology, and Microbiology, Auburn University,
Auburn, AL 36849.
- Features of sieve-element ontogeny in Ginkgo
biloba.
In an effort to enhance our knowledge of the phloem
of gymnosperms, an ultrastructural investigation was
conducted into the development of petiolar sieve
elements of Ginkgo biloba. As in the sieve elements
of other species, there is a stage of ER stacking
which precedes cytoplasmic lysis. In some cases the
ER forms concentric layers enclosing portions of
ribosome-rich cytoplasm. These concentric layers are
held together by bridges of 7 nm in length which