Abstracts of Papers - Harvard Forest - Harvard University

characteristic profile, or identifying fingerprint.
The composition of the profile differed
quantitatively and qualitatively among taxa. Taxa
with few triterpenes, tentatively interpreted as
primitive, occurred in dwarf forms, whereas
Madagascan taxa tended to possess high numbers of
triterpenes reflective of specialization. This
study supports the interpretation that laticifer
starch grain morphology and triterpene composition,
both gene mediated stable markers, can be employed
to determine and correlate phylogenetic
relationships between taxa of this complex genus.
MAKSYMOWYCH, ROMAN* Department of Biology
Villanova University, Villanova, PA 19085
MYRON C. LEDBETTER, Biology Department,
Brookhaven National Laboratory, Upton,
NY 11973.
- Fine Structure of Secretory Canals
in Xanthium pennsylvanicum Petioles.
Secretory canals, lined with an epithelium,
occur in many families, e.g. Umbelliferae,
Compositae. These canals extend continu-
ously through the root and shoot systems and
are known, in some cases, to secrete resins,
essential oils, etc. In Xanthium the canals
initials. Subsequent divisions lead to a
ring of 7-12 epithelial cells surrounding a
central cavity. During maturation the
epithelium becomes crushed and obliterated.
Canals were examined in petioles of Xanthium
pennsylvanicum (Cocklebur) plants grown
under long day illumination to maintain
vegetative growth. The fine structure of
the canal and its epithelium was studied by
electron microscopy of thin sections cut
transverse to the principal axis of petioles
from leaves in an early stage of develop-
ment. The canal proper is delimited by
walls of epithelial cells which protrude
into a scallop shaped cavity. In comparison
to the surrounding parenchyma, the epith-
elial cells are smaller, cytoplasmically
more dense, and less vacuolate. The epith-
elium contains pleomorphic starch-free
plastids with planar thylakoids frequently
stacked into granna; thus, the plastids are
presumed photosynthetically active.
Mitochondria are abundant and often dense.
The cytoplasm is rich in free polysomes, and
smooth endoplasmic reticulum predominates
LELAND C. MARSH AND JAMES L. SEAGO, JR.*. Department
of Biology, State University of New York,
Oswego, NY 13126.
-Adventitious rooting in Typha glauca under experimental
conditions.
Overwintering sterile plants from a single clone of
T. glauca were grown in nutrient solution with last
year's sterile stalk either submerged or emerged to
determine the effect on adventitious rooting. The
following results were observed: 1) Plants with
sterile stalks above the solution showed earliest
rooting (within 4 days). These plants produced
35-60 lateral roots per cm over the basal 10 cm of
the adventitious roots. 2) Plants with submerged
sterile stalks delayed rooting until 10 days, and
then only after new stalks with developed aerenchyma
had elongated 30 cm above the water surface. These
plants had fewer adventitious roots with less lateral
roots, except in the basal 1 cm. It was concluded
Developmental and Structural Section 25
that root development is related to the presence of
an air pathway from above the water surface to the
rooting zone at the base of the developing buds.
MAUSETH, JAMES D. Dept. of Botany, University of
Texas, Austin, TX 78712.-Development and anatom
of the parasite Tristerix aphyllus (Loranthaceae)
infecting Trichocereus chilensis (Cactaceae).
Many of the large columnar cacti Trichocereus
chilensis near Santiago are infected by Tristerix
(= Phrygilanthus) aphyllus. This is one of the most
highly reduced plants known: it is an endoparasite,
the flowers being the only parts of the plant ever to
emerge from the host, all the rest existing as an
endophytic haustorial system; roots, stems and leaves
are not produced. After infection, the parasite
spreads in all directions through the thick cortex of
the host, eventually reaching the vascular cambium
and conducting tissues. The parasite in this
invasive stage occurs as a "mycelium" of uniseriate
filaments that grow between host cells, deforming
them, but only rarely entering them. Later growth is
by apparently random cell division that produces
irregular parenchymatous strands. Ultimately xylem
and phloem are produced in these strands; the phloem
is normal but the xylem is almost pure parenchyma,
with only occasional idioblastic tracheary elements.
Strands close to the epidermis of the host are able
to produce adventitious flower buds that emerge
through either soft regions in the epidermis (the
areoles) or through accidental breaks in it. The
flower stalk may persist, forming a small perennial
inflorescence that has normal wood, phloem and bark
but is without leaves or chlorophyll. The portions of
the endophyte that produce these exophytic inflorescences
do not develop normal anatomy, but persist
as irregular parenchymatous strands with small amounts
of xylem and phloem. Host cells appear healthy and
normal, with no sign of damage caused by the presence
of the parasite.
MAZE, JACK. Department of Botany, University
of British Columbia, Vancouver, B. C. V6T 2B1,
Canada. - Explanations for leaf development.
The explanations offered for leaf development are
usually causal. The most common one is that leaf
development is the result of ontogenetic events
that are under genetic control, the cause in this
case being genetic. As well, kinetics, surface
area thermodynamics, and natural laws pertaining
to increasing disorder have been implicated in
ontogeny and may be presented as explanations of
leaf development. It is also possible to apply
teleological explanations to leaf development since
the most general form of a functional explanation
for leaf development is the same as the most general
form for the explanation for a vertebrate predator's
hunting behaviour, an undoubted teleological system.
It would thus appear that both teleological and
causal explanations may be applied to leaf
development. Of the causal explanations proposed,
all would seem to be based in natural laws.
However, causal explanations involving genetic
control of ontogeny, using natural laws pertaining
to chemical bonds, would not allow one to deduce
increasing complexity with development. To do so,
one must use natural laws pertaining to kinetics,
thermodynamics or increasing disorder.