von OStR J. A. Pfisterer
veröffentlicht in: Chronica Horticulturae 36/1, 9-12, 1996
Campusses of colleges and schools
usually are pretty boring. Plants growing there, normally are not
to be used for teaching. The purposes, they are selected for, are
low costs and how easy they will grow and will to be mainatined.
That is, why most of campusses can not be used to illustrate
different topics in biology or geography. On the other hand, if a
landscape architect accepts a teamwork with the teachers, a plant
assortment is possible, which is able to illustrate certain
subjects in plant geography and climatology, ecology and
evolution, molecular- and classical genetics and plant
physiology. The costs for a collection of plants according to
this purpose must not be higher. Plants that are interesting for
students and pupils will be more accepted and that is, why they
provoke less vandalism. Trees and shrubs can serve for more than
giving shadow, better climate or a green decoration.
The examples, cited here are
trees and shrubs for a temperate climate in Central Europe. They
are parts of a programme for teachers to show how a school campus
and the plants at the public parcs nearby can be used for lessons
in biology and geography. Plants that show similiar issues can be
found for every other climate too.
Different continents have
developed different varieties, even when the climate is similiar.
For example on the northern hemisphere grows the genus Fagus, on
the southern hemisphere it is replaced by the genus Nothofagus.
Another example is the mediterranean Macchia and Garrigue in
comparison to the woodlands of Southern California. Examples for
typical shrubs in Southern Europe are Erica arborea, which
produces the famous Bruyère-wood for pipe-bowls, Arbutus unedo,
or Euphorbia dendroides. In the New World the genus Euphorbia is
rare, and Erica does not exist. Arbutus exists in California with
a very similiar species (Arbutus menziesii), but Manzanita
(Arctostaphylos manzanita) is not found in the Old World, just a
creeping species (A. uva ursi) and the circumpolar exsting, also
creeping species A. alpinus. In the same way a wide range of
plants, typical for a certain biotope can be grown and be used
for instruction.
Adaptation to a certain climate
is not only a subject in geography but also in ecology. Typical
plants of arid and humid climates can be exposed, if the
microclimate at campus makes this possible. The same problem make
plants, adapted to acid or alkaline soils. A collection of those
plants is only in the cases to recommend, where a special soil is
existing at a campus. More easy to maintain is a collection of
different species of the same genus, adapted to diffent
altitudes. An example are the European species of the genus
Pinus: P. sylvestris, P. cembra, P. nigra, P. mugo. A collection
like this can be extended by deciduous trees typical for the
different altitudes. A similiar collection can be done with
typical Pine species for the different altidudes of other
continents like Sierra Nevada, Rocky mountains, Himalaya etc.
The biological discipline allows
more topics than climate, soil and water supply. If there is
enough space, examples of a biocenosis can be grown, for example
the shrubs and small trees of a hedgegrow or a coppice, typical
for the region. Eventually a similiar example from another
country can be grown for comparison.
More recommendet are singular
plants, which show extraordinary strategies to survive at an
extreme habitat. The weeping pine (Pinus wallichiana) collects
water from the fog. The long needles make the fog condense to
liquid water. The 'tears' dripping from the needles' tips supply
the roots with water.
Less spectacular are comparisons
between plants adapted to shadow and varieties adapted to bright
sun. Shadow trees are all species of Tsuga and Taxus, most of
Ilex and decidious plants like Rhamnus frangula from European
forests or the popular Japanese maple, Acer palmatum. Sun
worshipers have small leaves and are drought resistant like
Eleagnus angustifolia, Hippophae rhamnoides or Tamarix
parviflora.
Strategies to defend predators
can be chemical like burn (Urtica dioica), bad taste and smell
(Smphytum officinale, Solidago canadensis) or mechanical like
thorns and spines. Poisonous plants are not to be grown at a
school- or college campus. Interesting examples are plants with
red berries for feeding birds to get the seeds spread. Some of
these fruits taste awfully bitter. After beeing frozen the bad
taste has gone and the birds begin to feed of it. As a second
adaptation the seeds need frost for germination. European
examples are the 'bird's berry' Sorbus aucuparia or Viburnum
opulus which are not been fed before December. Other good
examples can be found in immigrated plants. Most of the newcomers
are not imported together with a native predator and the animals
in the new country are not adapted at their taste and avoid them.
Solidago canadensis is a typical example in Europe.
Spectacular examples for
mutualism are the relations between flowers and their
pollinators. All plants flowering in wintertime are adapted to
flies as pollinators. The same do species like Castanea sativa
and Sambucus nigra. Their nectar gets solid and the smell of
their flowers is attractive to flies but not very attractive to
human noses. Large flowers of Leguminosae like Wisteria can be
pollinated by butterflies and large bumblebees. Plants with deep
flowers are specialized in butterflies too. If their colour is
blueish like Bougainvillea, Buddleia, Plumbago or Verbena they
are attractant to daytime butterflies. Hawk moths are active
after sunset, they need white and yellow flowers that reflect dim
light sufficiently like Oenothera, Convolvulus or Lonicera
caprifolium. Flat flowers like wild Roses and Cistus can be
pollinated by bugs, the same do Umbelliferae. Dark red Flowers
are inattractive black for insects eyes, they are pollinated by
birds like Fuchsia and Hibiscus. Some Australian plants like
Callistemmon and Eucalyptus are pollinated by small Marsupials
and Selenicereus grandiflorus or Cobaea scandens are pollinated
by bats.
Adaptations also can be
demonstrated under evolutionary aspects. But there can be done
more. Living fossils like Ginkgo biloba, Metasequoia
glyptostoboides are well known and easy to grow. Sciadopitys
verticillata with its spectacular needles and the unusual xylem
architecture is another example. Relicted plants have a very
small natural habitat. A European exmple is Picea omorica which
grows naturally at a small region in former Jugoslavia. Araucaria
exelsa which shows the archaic Massard's Model at it best must be
grown indoors during winter time at temperate climates.
Another example are the species
of the Magnoliacea family like Magnolia or Liriodendron. The
plants show cone-like fruits and flowers which can be interpeted
as a link between Gymnosperms and Angiosperms.
Isolation can be demonstrated
with endemic plants, for example from Japanese archipelago. A
good example is the genus Acer with Acer carpinifolium,
cissifolium, japonicum, miyabei, nikoense, palmatum, rufinerve
and sieboldianum. Some species of cherry (Prunus) and apple
(Malus) also are endemic in Japan. Podocarpus macrophyllus is a
Japanese endemite of a genus, typical for southern hemisphere.
Another good example is
Sempervivum arachnoideum a perennial Crassulacea from European
Alps. Nearly every valley bares its own variety. Some dozens of
different varieties can be purchased in a good nurcery. There are
larger and smaller rosettes, leave's colour may be green, reddish
or dark red and leave's surface may be smooth or covered with
white hairs. The hairs may occur just at the leave's tips or
cover the whole surface, they may be longer or shorter, curly,
wavy or straight. Convergency can be demonstrated with similiar
plants of a different genus, for example Sempervivella or
Aeonium.
The most spectacular example is
the relict flora in Central Europe. During the Ice Ages plants
growing here got imprisioned between two barriers, one from the
north and one from the south. The mountains between Central and
Southern Europe spread from East to West and only three small
corridors kept open: the Basin of Paris, the Door of Burgundy
connecting the Rhine valley with the valley of river Rhône, its
width is only some kilometers and the valley of river Danube
leading to the Black Sea. For plants which have to migrate by
their seeds, its astonishing, that some of them did survive in
spite of these bad conditions. North American plants had no
similiar problems, Central Valley and the Great Plains are real
freeways for migrating plants. Similiar conditions had been at
Far East and the valley of river Dnjepr. This is why the floras
of North America, Far East and the region araond the Black Sea
are rich in comparison to the situation in Central Europe.
The subject can be illustated by
different topics. The ability to migrate can be demonstrated in
the genus Salix. The plants produce best flying seeds and there
exist more than 20 species in Europe. In comparison the Genus
Fagus survived in Europe with one single species. The same did
Abies, Larix, Picea, Carpinus. Plants which got extict in Central
Europe can be exposed in their species from Far East, North
America and eventually from the Black Sea region. Some examples
are popular plants in European parcs like Calocedrus,
Chamaecyparis, Catalpa, Liquidambar, Liriodendron, Magnolia,
Paulownia. Another good example is the genus Acer. In Central
Europe survived three species (A. campestre, platanoides,
pseudoplatanus) Sothern Europe has some more (A. monsplessulanum,
opalus, sempervirens). In North Amerika survived more than 20
species. The same did the genus in the Far East and ther are some
more endemites at the Japanese archipelago. Most of these plants
are very popular in public parcs. Ans these parcs can be made
more attractive for visitors if the trees get small panels with
some more information like botanical name and origin.
Crossbreeding may be done with
different fast growing herbs, good examples are Mirabilis, Dahlia
and Antirhinum. F1-Hybrids are attainable of different
ornamental herbs, their seeds can be used for a F2-generation.
Woody plants can be used for demonstation of mutation and modification. Good examples are variegated plants and Purpurea- and Aurea-varieties. White spotted leaves depend on a mosaic-gene. Red leaves produce anthocyane, the colour is deposited in the vacuole. In yellow leaves the production of chlorophyll is stopped by high UV-radiation. The synthesis of the carotines is not reduced by light, so the leaves occur yellow. The three variations are the results of mutations. But there is a conspicuous difference between shadow- and sunleaves. In the shadow leaves are less red or yellow than in the sun, what can be interpreted as a modification. Variegation does not depend on light exposure, so this mutation is stable against environmental influences. From Acer negundo cultvars exist in all varieties necessary for demonstration. Many cultivars depend on somatic mutations which occured at a single branch. The mutation did not occur during a meiosis but during a normal mitosis.
Another good example are
chimaeric plants. The cultivars are the result of a craft when
tissues of both plants produced a joint bud. Best example is
+Laburnocytissus adamii from a craft of Cytissus purpurea on
Labrunum anagryoides. The large shrub may bloom with both types
of flowers at the same branch. Less spectacular and more
difficult to explain are the roses Rosa feotida bicolor and Rosa
omeiensis pteracantha. R. foetida may bloom at the same shrub
with yellow, red and bicolored flowers and R. omeiensis may bloom
with flowers with four and five white petals at the same branch.
The rose cultivars are not the result of a crafting accident.
It is more interesting to
understand mutations at a molecular level. For this purpose some
good examples exist. The different cultivars of Acer negundo may
be interpreted as mutations of certain genes i.e. expression of
certain encymes or the activity of a repressing or operating
gene. Repression of chlorophyll leads to yellow leaves,
activation of a synthesis of anthocyanes leads to red colours.
White spots are the result of a mosaic gene etc. The highest
number of different cultivars may exist in Fagus sylvatica.
Best examples can be found in
roses. Number and colour of petals can be interpreted as
mutations and may be tested by easy going experiments.
Multiplication of petals can be done by two different mutations,
duplication of a petal and/or the change from a stamen to a
petal. Petals that have their origin from a stamen can be
recognized macroscopical. They are curled, often not symmetrical
and the most inner leaves may bear a shriveled rest of the
pollinium. Another popular alteration is a green strip at the
outer petal. It is the result of an event during flower
develpoment. In the bud one or some cells from sepalic tissue
became part of the outermost petal.
In white roseflowers all genes
for the synthesis of anthocyane are active except the very last
one. All preliminary substances, which are transparent can be
proved by a cromatogramme. The gene-repression can be lifted by a
very easy experiment. After a rainfall white roses get wreckled.
The red spots are the result of a fungus in cooperation with UV
light. If white flowers are hurt with a fine needle, they will
produce their wreckles under UV light. If the flowers are covered
with a jar, the spots get brown. In this case the fungi just
destroyed the tissue, they could not provoke the coulouring
reaction.
A good example for a sport is a
crossbreeding of David Austin. The rose Charles Austin blooms in
brilliant salmon-pink. The colour is the result of a mixture of
yellow carotines and red anthocyanes. A cross section through a
petal observed under a light microscope reveals yellow plastids
and red vacuoles. From this rose exist two sports. Yellow Charles
Austin lost the ability to produce red colour. Proud Bride blooms
in a rich pink. In this case the ability to produce carotines in
the petals is gone.
Rosa Mundi is a medieval sport of
a Rosa gallica. The petals bear white and red stripes. The gene
is crossbred in a number of new roses. There exist varieties in
white and red (for example Paul Pichard, Tanne) and yellow and
red (for example Caribia, Wheatcroft).
Roses with different colours of the inner and the outer side of their petals bear the gene from Rosa foetida bicolor and Roses like Regensberg (Kordes) produce the red colour just under UV light, without the exctetions of a fungus. The outer part of the petals are pink. Where the petals are covered by the next one, the flower is white.
Some humoral mechanisms
controlling a plants growth can be demonstrated and understood at
trees and shrubs. Reactions like epinasty, water balance or
dominance of the terminal bud are some examples. Constant wind or
light from one side are effects able to change a trees habitus as
well as root damage or senility.
Another good example are
reactions by changed tension, for example reiterations. A
reiteration is the repetition of a tree's crown, originating from
an advetitious or proventitious bud. The structure occurs at
braches and stems that are bent down. The increase in tension
causes a disarrangement in the allocation of ions at cell
membranes. The disarrangement of ions is a signal for the
activity of cell division. This is why new bud occur at the point
with the highest tension. Similiar reactions are the production
of recation wood round a wood or for epinastic movements.
A lot of information can be given about plants at a campus as at a public parc
as well. And a campus should be
planned according to the age and the lessons of the students to
be taught there. That is why a generalized pattern is not to be
given.
A plant collection, selected for
a landscape to be planned anew, depend on the purposes, the parc
has to serve for. It is more difficult to accomplish a parc, that
is already planned and planted. a regardful planning will
consider the trees and shrubs already growing there. So the
existing treees will be the beginning of the new planting. If
there are growing native plants, the best individual oif each
species may be kept and be accomplished with companion plants of
the same ecosystem to expose a certain ecological situation. A
Norway- and a Sugarmaple may be completed by less popular species
of the same genus. A drought resisting Eleagnus or Eucalyptus may
be associated to other varieties of the same ecotype like
Hippophae or Tamarix and a Bald Cypress (Taxodium distichum) ma
provoke the installation of a pond to make the tree produce its
famous respiratory roots.
Jochen A. Pfisterer, Biologist,
gardener, expert public for
trees care,
Friesenbergstraße 27,
D-76530 Baden-Baden.
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