Abstracts of Papers - Harvard Forest - Harvard University

in the septa between the carpels. Although crystal sand
can be found in cells of the ovary and prismatic crystals in
leaf idioblasts, only druses are found in the zones asso-
ciated with abscission or dehiscence. The druses are found
in the abscission zones at relatively early stages long
before abscission is to occur. The druses (a multiple array
of twin crystals arranged in a spherical space) develop
within the vacuole of the crystal idioblasts. The druses
vary somewhat in size and morphology and in the structure
of the individual crystals which make up the druse. In
some cases crystals are sharply pointed, in other cases they
are less pointed or even rounded. As the crystals of the
druse develop some appear to press through the cytoplasm
and grow near the cell wall. Later in development a cell
wall-like sheath grows around the crystal. Whether this is a
response to the crystal penetrating the cytoplasm and
appressing the cell wall is not yet clear. The cell wall-like
sheath can easily be seen by electron microscopy and
appears similar to the primary wall. Isolated crystals may
still be encased by this sheath. Once the sheath is
complete the crystal is sealed off from the remainder of
the still living cell. After the organ has abscissed the
crystal remains just below the scar left by abscission. The
concentration of crystals at this point suggests a possible
protective role for the crystals. Obviously this may be a
secondary "function" in that the crystals may play a more
meaningful role in calcium metabolism prior and during the
formation of the abscission layer.
JENSEN, WILLIAM A.*, MARIE MIZELLE, RAVINDER
SETHI and MARY ASHTON. Department of Botany,
University of California, Berkeley, CA 94720.
- Pollen development in wheat treated with a
chemical hybridizing agent.
Triticum aestivum seedlings were treated with a
chemical hybridizing agent developed by Rohm and Haas
Chemical Company known as RHOO07. It caused the
pollen to abort without markedly affecting the fer-
tility of the ovule. Ultrastructural and histo-
chemical studies revealed the compound specifically
inhibited the formation of sporopollenin. This
inhibition was not complete but the pollen in treated
plants laid down a wall only 1/3 as thick as that
found in the control. Histochemical studies indicate
that it is not the synthesis of the carotene subunits
but the polymerization step that is inhibited.
JENSEN, WILLIAM A.*, MARIE MIZELLE, RAVINDER SETHI
and MARY ASHTON. Department of Botany, University
of California, Berkeley, CA 94720. - Ultrastructural
study of pollen development in wheat.
A study of pollen development in Triticum aestivum
was made using the electron microscope. The study
began with the microspore mother cell and continued
to the mature pollen. Stress was placed on the
changes in the cytoplasm during the various developmental
stages, as well as oni the wall. Marked
changes in ribosome number, plastid size and shape,
and amounts of ER were noted at various stages.
The quantity of wall deposited was also studied in
detail. This study forms the foundation for the
data presented in the subsequent work on a chemical
hybridizing agent.
KANE, MICHAEL E.* and LUKE S. ALBERT. Department
of Botany, University of Rhode Island,
02881. - Effects of ABA on-heterophylly
Kingston, RI
and stomatal
development on submerged juvenile shoots of
Myriophyllum heterophyllum Michx.
In the heterophyllous aquatic angiosperm M. hetero-
Developmental and Structural Section 23
phyllum, submerged juvenile shoot apices develop dis-
sected astomatous leaves that are composed of fili-
form divisions consisting of a compact mesophyll. In
contrast, aerial juvenile apices develop smaller and
thickened pinnatisect leaves which bear adaxial sto-
mata in a cutinized epidermis and lacunae within the
mesophyll. Results of recent investigations on the
physiological control of submerged and emergent forms
in two other heterophyllous aquatics suggest a role
for water-stress induced formation of abscisic acid
(ABA) in the development of aerial leaf morphologies.
To determine whether ABA also plays a role in the de-
velopment of the aerial juvenile phase of M. hetero-
phyllum, axenic cultures of the submerged juvenile
phase were grown in a liquid medium consisting of
Murashige and Skoog salts, vitamins, and 3% sucrose
with or without ABA (10-9 to 10-4M) at 25 C in a 16
hr photoperiod (PAR; 200 uE m-2s-l) for 10 days. Con-
trol plants produced astomatous leaves typical of the
submerged growth phase while exposutre to 10-6, 10-5,
or 10-4 M ABA induced the formation of leaves morpho-
logically and anatomically similar to those on aerial
juvenile shoots. The influence of ABA on adaxial
stomatal development was evident by observed increases
in stomatal densities with hormone concentration (23,
100, 150, and 154 stomates/mm2 for plants exposed to
10-7, 10-6, 10-5 and 10-4 M ABA, respectively.) The
hormone ABA therefore appears to play an important
role in the control of heterophylly and stomatal
development in an increasing number of aquatic
angiosperms.
KAUL, ROBERT B. School of Life Sciences,
University of Nebraska, Lincoln NE 68588.
-Inflorescence architecture and evolution in
Asiatic Fagaceae.
More than 200 Far Eastern species of Castanea,
Castanopsis, Lithocarpus, and Quercus have been
examined. Flowers are borne on spikes that are
axillary to leaves and bracts of the current and
previous seasons' stems. The spikes are often
unisexual and male spikes greatly outnumber females
on a tree. Some spikes, however, are androgynous,
gynecandrous, or androgynecandrous, and all three
conditions can occur on a single tree. Various
degrees of separation of the sexes and of aggrega-
tion of spikes into reproductive short-shoots exist.
Some short-shoots have abortive apices and others
produce monopodial continuation growth. Sometimes
both kinds occur on the same individual, in which
cases the determinate short-shoots are below the
indeterminates and ordinarily bear only male flowers;
the determinates usually bear a few female flowers
in their distal spikes. More or less paralleling
these phenomena is reduction from foliage leaves to
bracteoles on the short-shoots. The most extreme
condition occurs in Quercus, where the short-shoots
are always unisexual, determinate, and only bract-
eolate, and male flowers are borne on pendulous
spikes (catkins).
KAUSCH, A.P.* and H.T. HORNER. Department of
Botany, Iowa State University, Ames, IA 50011.
- Increased nuclear DNA content during raphide
crystal idioblast development in Vanilla plani-
folia L.
Files of calcium oxalate raphide crystal idioblasts
are formed in the cortex of adventitious roots of
Vanilla planifolia L. Idioblast initials are first
recognized by intense fluorescence of the cytoplasm
with the acridine orange method. Nuclear and nucleo-