Abstracts of Papers - Harvard Forest - Harvard University

RUGENSTEIN, SEANNA R. Department of Botany,
Louisiana State University, Baton Rouge,
LA 70803.
- Seed testa patterns in Cercideae
(Caesalpinioideae: Leguminosae).
The caesalpinioid legume tribe Cercideae contains
six genera in two subtribes. Scanning electron
microscopy was utilized to study the anatomy of
seeds of 60 species representing 25% of the species
in the largest subtribe and 83% of the species
in the second. Several features of papilionoid
legume seed anatomy have been shown to have
taxonomic utility (Gunn, 1981; Kupicha, 1977;
Lersten and Gunn, 1982). It was determined,
during this study, that testa patterns in
Cercideae differed in size rather than basic
configuration, from those on papilionoid
legume seeds. The basic testa patterns
in Cercideae, as in papilionoid legumes,
are papillose, reticulate, and foveolate.
Other features of Cercideae seed anatomy,
such as size and shape of hilar tongue,
hilar groove, and micropyle, were also
examined. The distribution of these anatomical
features of the Cercideae seed seem to be
indicative of subtribal and subgeneric
taxonomic affiliations.
RUSSELL, SCOTT D. Department of Botany and
Microbiology, University of Oklahoma, Norman, OK
73019 - Gametic fusion in Plumbago zeylanica:
Ultrastructural evidence for gamete recognition and the
preferential transmission of sperm plastids into the
zygote.
The mature microgametophyte of Plumbago zeylanica
contains two dimorphic sperm cells which may be identi-
fied by differences in both morphology and cytological
content. One of the two male gametes is associated with
the vegetative nucleus throughout its later development
and is distinguished by the presence of a 30 micrometer
long cellular projection which wraps around the vegetative
nucleus. Cytological content of this sperm cell includes 0
to 2 plastids and an average of 256 mitochondria. The
other sperm cell is connected to the first sperm by
plasmodesmata, is not closely associated with the vegeta-
tive nucleus and lacks a prominent cellular projection. The
second sperm cell contains 8 to 48 plastids and an average
of 40 mitochondria. Upon discharge of the gametes from
the pollen tube, both sperm cells are deposited in an
intercellular region within the female gametophyte,
located between the egg and central cell. The distinctive
morphology of sperm plastids after fertilization can be
used as a naturally occurring cytoplasmic marker to deter-
mine which of these two sperms fuses with the egg and
central cell. Evidence to date has suggested a preferential
pattern of fusions between the plastid-containing sperm
and the egg cell, transmitting a number of plastids into the
incipient embryo. The other, plastid-poor sperm fuses with
the central cell, transmitting numerous mitochondria into
the incipient endosperm. This preferential pattern of
organelle inheritance strongly suggests that gametic fusion
in the megagametophyte is not random in P. zeylanica.
These results provide evidence for the presence of a final
putative barrier to reproduction consisting of a gamete-
level recognition system which may operate in the male
and female gametes of this angiosperm.
SANGSTER, ALLAN, G. Division of Natural Sciences,
Glendon College, York University, Toronto, Ontario,
M4N 3M6
-Anatomy and silica distribution patterns in root
and rhi zome of the grass Mi scanthus sacchari fl orus .
Developmental and Structural Section 31
Anatomy and deposited silica distributional patterns
were investigated for the root and rhizome by means
of scanning electron microscopy and energy dispersive
X-ray microanalysis. In the root, silica deposits
were confined to the single-layered endodermis in the
form of large aggregates. In the rhizome, silica was
present in two concentric regions consisting of the
outer endodermis and the cells bordering the inner
central cavity. Both these regions were several-
layered, and the deposits were part of the cell wall
layers rather than projecting aggregates. In both
organs, a perivascular distribution pattern was
evident, single-layered in the root but multi-layered
in the rhizome. The root pattern is consistent with
that investigated for other genera of the tribe
Andropogoneae, as is the endodermal deposition site
for the rhizome. However, rhizome deposits differ
in form from other genera, and deposition around the
central cavity has not been encountered previously.
SCRIBAILO, ROBIN W. and U. POSLUSZNY, Department
of Botany and Genetics, University of Guelph,
Guelph, Ontario, Canada NlG 2W1
- Morphology and establishment of seedlings of
Hydrocharis morsus-ranae.
Hydrocharis morsus-ranae is an introduced aquatic
plant species in North America. Little is known
concerning the nature and morphology of seedling
germination in this species. Consequently it has
been assumed that Hydrocharis morsus-ranae must
overwinter primarily through the production of large
numbers of vegetative propagules. As part of a
continuing study of this species an S.E.M. and field
investigation of the seed and seedling morphology
were initiated to contribute to the limited know-
ledge of germination patterns within this genus and
the Hydrocharitaceae as a whole. The seeds of
Hydrocharis morsus-ranae are highly unusual morpho-
logically having their entire surface covered with
hollow spiraliform tubercles. Germination occurs
when the embryo of the exalbuminous seeds elongate
splitting the tuberculate testa. The buoyant
developing embryos then rise to the surface and the
first foliage leaves emerge from a highly modified
cotyledonary sheath. The young seedlings undergo
several growth phases in which they first appear
lemnid in habit before attaining their character-
istic reniform leaf shape. In the field, substantial
numbers of Hydrocharis morsus-ranae seedlings were
found germinating among the turions of the same
species. It is likely that reproduction from seed
is more important in this species than previously
thought.
SHULTZ, LEILA M. Department of Biology, Utah
State University, Logan UT 84322. - Leaf vessel
measurements in desert perennials.
The relationship of habitat and leaf vessel
measurements is explored in comparative anatomical
studies of sixteen closely related taxa (Artemisia
spp.) from the cold deserts of western North America.
Data are presented which document changes in vessel
structure as well as relative volumes of tracheary
tissue in habitats which are defined by a gradient
of increasing aridity. As might be expected, vessel
diameters decrease and width of cell walls increase
with increasing aridity. Few studies, however, have
addressed the possibility of volumetric changes in
tracheary tissue. The relative volume of xylem to
total tissue volume in the leaf appears to be a
sensitive indicator of water stress. That ratio is
presented and discussed here as a Xeromorphy Index.