The Botany Bit
Evolution, propagation of the species, or whatever you want to call it,
has long depended on the union of two different individuals. This is as
true in the botanical world as it is for insects, birds and animals. In
almost all cases these are male and female individuals. Furthermore, in
plants and animals, one of them, the female germ cell is fixed, not mobile
that is, whereas the other, the male is mobile, and so it is with plants
in almost all cases. Although the male is 'mobile' he needs help to get
We all know the basic parts of flowers such as the petals, sepals and
pedical or stem.
In flowers this is the stamen which consists of a filament (or stalk)
upon which is the anther where the pollen develops.
This consists of a carpel which is a style (or stalk) upon which is a
stigma on to which pollen will be placed. When that happens the stigma
stimulates the pollen to seek the ovary by growing down the style. By
the way, when a plant has more that one carpel (and most do) one or more
carpels are called a pistil.
In these modern times we all know about DNA for various reasons. We also
know that genes are a component of DNA, and that these genes contain the
specification for their parent organism.
Dominant - where one gene swamps another, for example RED dominant to
the opposite where the recessive gene WHITE is recessive to RED.
Chromosomes occur in pairs usually. In the formation of gametes one of
each pair goes to each germ cell at random. When the chromosomes form
germ cells genes are interchanged between the two members of a pair. However,
although the points at which their interchange take place is again a matter
of chance and the genes of each pair go to the germ cells independently
of each other, there is a tendency (if they lie close together) for them
to keep together as they go to the germ cells. This is known as LINKAGE.
Science can be thought of as common-sense based on exp[eriment.
Chromosomes with similar numbers will probably cross
Seed - variable germination due to dormancy. Need os some special condition
such as pulp fermented - Sow in box, small peebles pushed in, seed drops
Damping Off - Pythium de baryanum fungus (Cheshunt Compound (cuprammonium
remember 'dahlia/sunflower' example and the 'blood'
Seed - may need refrigeration to keep or even to activate.
Pollen - is the male gametes, not self-mobile, as in animals, so needs
The sticky substance on the stigma activates pollen.
Devices to prevent self-fertilisation in some plants - such as different
ripening periods for pollen and stigma, or incompatibility factors which
prevent pollen fertilising. Most often found in perenials which, being
long-lived, can insist on cross-fertilisation. Rogues are a danger to
self-fertilised plants as the stock will not remain pure.
Germination - remember epiphyllum seed germinating in fallen fruit in
weeks (3) where it took years (3) before. Correct temperature may be important.
Temperature change can kill.
Germ Cells or Gametes
After fertilisation the new cell remains fixed for a time to the tissue
producing the female germ cell, and undergoes further development before
parting from mit and beginning life on its own.
Any mention of plant breeding should include some reference to Gregor
Mendel (1822-1884), an Austrian monk. He embarked on a series of experimental
studies on plant breeding involving the edible pea. He conducted various
experiments on smooth and wrinkled peas but the best known and influencial
one relates to crossing a tall variety of pea with a short one, and observing
the ratio of one to the other in the progeny. From this work came his
Laws of Heredity.
He found that, in the first generation which became known as F1, that
only tall ones appeared. So the story goes, this led Mendel to recognise
'tallness' as the dominant factor, and 'dwarfness' as the recessive factor.
It should be noted that his wise choice, the pea, did not involve colour,
scent, shape or size, only tall and short.
He bred another generation from that first F1 and obtained a second filial
or F2 generation. In this he found that plants were not all tall as in
F1, but were in certain ratios for tallness, shortness, and breeding from
'true'. These ratios are usually illustrated by reference to the colours
RED and WHITE, but the same holds whatever the factor.
If we symbolise these as R for red and W for white, then crosses become
RR for two red crosses, and WW for two white crosses. A red and a white
cross would be designated as RW.
From these crosses we get Mendel's Law of Heredity which is widely recognised,
and the foundation of genetics and inheritance. His work related to tallness
and shortness, remember.
The chart on the left shows that a quarter of them are Red, half are Red/White
(=pink), and a quarter are white. These ratios demonstrate that the frequency
of Reds and Whites occur by chance as can be demonstrated by tossing coins
woth head and tails corresponding to the two choices of Red and White.
After ???XX tosses you will get ???. Coming back to the peas, the previous
ratios continue in further crosses when the attributes reduce to a quarter
of these ratios, or to one sixteenth (a quarter of a quarter). The effect
of this is that large numbers of plants (ie hundreds) become involved
which is not practical for us amateurs. However, knowing what effects
may be expected when crossing two different plants is helpful.
If we cross two plants of the same species, for colour, size and/or shape,
we, too, can discover which is the dominant factor. This shows in the
F1 generation. Crossing these again in a second or F2 generation the gives
the Mendel Ratios of quarters and halves.
1 - All American pictures came from http://pdphoto.org and are public domain
- an excellent site worth looking at.
2 - Ladybird on 'Biological Control' courtesy of Henry Doubleday Research
3 - Cryptolaemus larva and Lacewing pictures from Wiki-pedia.org
4 - Augmentation, Classical Biological Control, and Conservation paragraphs
from Biological Control - Cornell University, Weeden, Shelton, Li, Hoffman
5 - Matt Pentecost for some of his Scottish photographs.
6 - Douglas E Wilcox for some of his Scottish photographs
see more at http://www.gla.ac.uk/medicalgenetics/gallery.htm
NOTE: the webmaster has acknowledged as best he could and consulted where
possible. If anything is unsatisfactory it will be put right - let the
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