Download Woon Teck Yap Section: M1-3, E53-220 Meeting 2 Out-of

Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
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Introduction
Artificial fertilization has long been employed as a method of producing new colour
variations in ornamental plants. It has been observed that whenever members of the same
species were cross-fertilized, particular hybrid forms appeared with astounding
consistency and regularity.
In an attempt to elucidate the mechanism behind this
phenomenon, experiments involving the hybrids and their progeny were undertaken and
are described herein.
Before this, many other researchers such as Kölreuter, Gärtner, Herbert, Lecoq and
Wichura have spent much time trying to determine the mechanism of inheritance behind
hybrid reproduction. In particular, Gärtner has made some very interesting and valuable
observations in Die Bastarderzeugung im Pflanzenreiche.
In addition, Wichura has
recently published some results regarding his research on the hybrids of the Willow. Due
to the fact that research on hybrids is time-consuming, laborious and difficult and that
observing them requires a large span of time (several years or more), no one has yet come
up with a suitable working model or “universal law” to describe the formation and
development of the botanical hybrids. Such a model can be formulated if and only if
detailed experiments have been made on a variety of plant species.
At the moment, there are no published records of any experiments that have been
adequately and satisfactorily carried out to determine the number of different forms of
hybrid progeny and the separate generations in which these progeny occur. In addition,
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Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
statistical analyses of the relationships between the various forms of hybrid progeny have
not yet been performed. Such detailed theoretical and experimental data is required
before one can answer any questions regarding the history and formation of any living
species on Earth.
This paper describes the results and conclusions of such a detailed experiment on a small
plant group, which was observed carefully and painstakingly over a period of 8 years. It
is left to the reader’s judgement as to whether the experiments were suitably planned,
conducted and executed, with regarding to obtaining the desired results and detailed
analyses.
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Materials and Methods
2.1
Growth of Pea Plants
All pea plants were either grown in garden beds or pots. Pea plants were maintained in
their natural upright position by means of sticks, branches of trees or string stretched
between them. For each particular experiment, i.e. set of cross-fertilization experiments,
a specific number of potted pea plants were placed during the blooming period in a
greenhouse to serve as controls for the determination of the effects of any possible
disturbance by insects, i.e. unwanted, random cross fertilization by insects.
2.2
Selection of Suitable Pea Plants
All experimental plants described in this paper are of the genus Pisum, possessed
constant differentiating characteristics and produced hybrids and offspring that showed
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Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
no marked decrease in fertility in successive generations. All experimental plants were
derived from 34 more or less distinct varieties of peas obtained from several seedsmen.
These peas were grown and the resulting pea plants were then subjected to a 2-year trial,
in which the characteristics of the latter were carefully observed. 22 of these pea plants
that exhibited highly similar characteristics were then selected and cultivated for the
entire 2-year period. All pea plants used in subsequent experiments were then derived
from these 22 plants.
2.3
Characteristics of Pea Plants Examined
7 different characteristics that were easy to follow and classify were chosen for careful
observation in the pea plants that were cultivated and are listed below:
1. Surface morphology of ripe seeds: Seeds were either classified are round and
smooth or irregularly angular and deeply wrinkled. Seeds that were classified as
round and smooth were either round or roundish and any depressions that
occurred on the surface were always shallow.
2. Colour of the seed albumen (endosperm): The colour of the endosperm of the
ripe seeds fell into either one of two categories – green or yellow. The endosperm
was classified as green so long as it possessed a more or less green tint while it
was classified as yellow if it was either pale yellow, bright yellow or orangecoloured.
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Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
3. Colour of the seed-coat: The colour of the seed-coat fell into either one of two
categories – white or grey, grey-brown, leather-brown (with or without violet
spotting). White seeds coats were constantly correlated with white flowers being
observed in the pea plants while grey, grey-brown and leather-brown seed coats
constantly correlated with flowers in which the standards were violet and the
wings were purple. In addition, the axils of the leaves of these latter pea plants
possessed a reddish tint. All grey seed-coats, upon boiling in water, turned dark
brown.
4. Morphology of ripe seed pods: Seed pods were either inflated and not contracted
in any places or more or less wrinkled and deeply constricted in the areas between
the seeds.
5. Colour of unripe seed pods: Unripe seed pods were either light to dark green or
vividly and intensely yellow. For yellow unripe seed pods, the stalks, leaf-veins
and calyx of the corresponding pea plants were also coloured yellow.
6. Position of flowers: Flowers were either classified as axial or terminal. Axial
refers to flowers being distributed along the main stem while terminal means that
the flowers were bunched at the top of the stem and arranged in a false umbel, in
which the upper part of the stem was more or less widened in cross-section.
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Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
7. Length of stem: The length of the stem was either categorized as long or short.
Long stems refer to those in which the long axis was around 6 to 7 feet while
short stems refer to those in which the long axis was around 0.75 to 1.5 feet.
2.4
Production and Propagation of Hybrids
Each pair of differentiating characters described above (refer to Section 2.3) were united
into one pea plant by cross-fertilization of two pea plants which exhibited constant
differentiation in one of the two forms of a particular character.
In total, 7 experiments were carried out in order to unite the 7 different characters under
investigation.
The details of these 7 experiments are listed in Table 1.
Fertilization/cross-fertilization was carried out on only the most vigorous members of a
large number of pea plants or the same variety. In experiments involving reciprocal
crossings, if a particular pea plant served as the seed-bearer in one set of fertilizations,
then it was used to provide pollen in the other set of fertilizations.
Table 1: Details of the 7 experiments in which the 2 different forms of a particular
character are united in the same plant by cross-fertilization
Experiment
1
2
3
4
5
6
7
Number of fertilizations
60
58
35
40
23
34
37
Number of plants fertilized
15
10
10
10
5
10
10
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Woon Teck Yap
Section: M1-3, E53-220
Meeting 2
Out-of-class Exercise 2
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