Abstracts of Papers - Harvard Forest - Harvard University

GAGNON, DANIEL and GARY E. BRADFIELD. Departement
des Sciences biologiques, Universite du Quebec a
Montreal, Montreal, PQ H3C 3P8; Department of
Botany, U.B.C.,
- The vegetation
Vancouver, BC V6T 1W5.
of west central Vancouver Island,
B.C.: a gradient analysis.
Forests of the study area are dominated by Thuja pli-
cata near the coast, and increasingly by Pseudotsuga
menziesii progressing inland. The vegetation and
soils were sampled in 172 plots to determine which
environmental gradients could explain the observed
patterns. Following successive reciprocal averaging
ordinations, six distinct vegetation groups and 24
community types were defined. An ordination (RA) of
only the modal communities suggests that the predomi-
nant vegetation pattern is under control of a "com-
plex" precipitation - continentality climatic gra-
dient. Variables strongly correlated with the ordi-
nation's major axis were: positively, distance from
the coast and fire disturbance, and negatively, wind
disturbance and thickness of organic horizons/rooting
depth ratio. Vascular species richness also increa-
sed with distance from the coast.
GALEN, CANDACE. Department of Botany, University
of Texas, Austin, TX 78712
- Ants, bumblebees, and seed production in floral
scent morphs of Polemonium viscosum.
Plants of Polemonium viscosum have flowers which are
either sweet or skunky-scented. The effects of
bumblebee pollinators and ant nectar thieves on seed-
set in these morphs were examined at 3528 m and 3640
m in alpine Colorado. The following patterns were
found.
Bumblebees accounted for 90% of the total pollin-
ation at 3640 m, but only 50% of that at 3528 m. No
differences in average seed-set of sweet and skunky
morphs resulted from bumblebee visitation at either
altitude.
Ants reduced seed-set of sweet flowers at both lo-
cations by negating the pollination effectiveness of
bumblebees. Damaqe to floral tissues by ants prevent-
ed subsequent fertilization or survival of ovules.
Ants did not alter seed-set of skunky flowers.
Activities of bumblebees and ants are therefore
likely to influence success of P. viscosum. While
ants may have significant effects on frequencies of
floral morphs at both altitudes studied, similar con-
clusions cannot be drawn about bumblebees from this
experiment.
GOVIL, SUDHA R. AND HARENDRA N. PAMTEYB
Department of Botany, Banaras Hindu
University, Varanasi - 221005,India.
- Studies on the crop-weed interaction.
The interaction of Cyperus rotundus(weed)
with wheat and maize crops was studied at
three densities and five ages under field
conditions. There was 37-40% reduction in
the weed density as the nuPber of crop
plants (27 to 81 planLas m in wheat and
4.5 to 13.5 plants m in maize)increased
in the experimental plots. In wheat -
Cyperus interaction, peak values of dry
weight, leaf area, chlorophyll and N,P, K
contents of the crop and weed plants
showed 45-74% and 6-17% reduction respec-
tively. Similarly in the maize-Cyperus
interaction, the crop suffered mre (1&T7-
7 5%) than the weed( 8-43%) . During the
Ecological Section 47
cropping cycle, in both maize and wheat
fields, weed parameter values were higher
relative to corresponding measures for
crops in the earlier phases for dry matter
production, leaf area index and standing
crop of chlorophyll. The trend, however,
was reversed at the later ages due to
suppression of weeds by the crop, and the
onset of weed' s senile stage. It is
concluded that this serious perennial weed
is equally harmful to both rainy and win-
ter season crops and increasing density
of crop plants proves to be more harmful
for themselves thar to the weed.
-Department of Botany, U.P.College,
Varanasi-221002, India.
GROVE, KATHRYN F. Department of Botany,
University of Iowa, Iowa City, IA 52242.
- A cryptic stylar outcrossing mechanism in an
autogamous tropical herb:
The stigma of Spigelia humboltiana Cham. & Schlecter
(Loganiaceae) has a proximal region which is self-
pollinated before anthesis and a distal region which
may receive cross pollen. Thus, cross pollen appears
to have a twofold disadvantage: it arrives on the
stigma after self pollen and further from the ovary.
Fluorescence microscopy was used to discoVer whether
these apparent disadvantages to cross pollen are com-
pensated for by differences in the timing of germina-
tion or pollen tube growth of cross vs self pollen.
Studies of open- and hand-pollinated flowers reveal
that: 1)pollen does not germinate on the selfing
region of the stigma until about 5 hours after
anthesis; 2)pollen on the stigmatic tip, however,
germinates promptly; 3)the earlier cross pollen
arrives on the stigma, the greater are its chances of
growth beyond the selfing region before self pollen
germination; 4)some natural cross-pollinations are
ineffective because pollen arrives too late; 5)
there are no differences in self and cross pollen
tube growth rates. Cryptic stylar outcrossing mech-
anisms may occur in other autogamous species.
HANYCH, DAVID A. Dept. Ecology & Behavioral
Biology, University of Minnesota, Mpls., MN 55455.
- The relation of seed size and seed weight to
seed set in the white campion, Lychnis alba
(Caryophyllaceae).
Mature Lychnis alba capsules were randomly and
selectively collected from an old field population
during two sampling years (1981 & 1982). The mature
seeds from each capsule were dried to constant weight
and then sized by measuring the axis parallel to the
hilum using a dissecting microscope equipped with an
ocular micrometer. A significant positive correla-
tion was documented between mean seed size and mean
seed weight on a per capsule basis during both
sampling years. However, both mean seed size and
mean seed weight were inversely related to the number
of seeds per capsule during both years. Similar
statistically significant trends were observed among
capsules collected from individually marked plants
during 1982. Since seed weight may be considered a
measure of the energetic investment in a seed by the
plant, the variance in relative investment per seed
as a function of capsule seed number may reflect a
reproductive effort characterized by variable
resource allocation to seeds within individual fruits.