British Cactus and Succulent Society

Highlands & Islands Branch

Appendix-2

 
 

This is another collection of detailed explanations of relevant subjects, some gleaned from various sources as shown at the foot of it. It is hoped this will make them more accessible and not clutter up other parts of the site.

 
 
  • The Botanical Bit
  • The Genetics Bit
  • Mendel
  • Acknowledgements
  •  

     

    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 there.

    We all know the basic parts of flowers such as the petals, sepals and pedical or stem.

    Male Part
    In flowers this is the stamen which consists of a filament (or stalk) upon which is the anther where the pollen develops.

    Female Part
    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.

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    Genetics Bit
    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.

    Genes

    Dominant - where one gene swamps another, for example RED dominant to WHITE.
    Recessive
    the opposite where the recessive gene WHITE is recessive to RED.

    Chromosomes
    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.

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    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 into cracks.
    Damping Off - Pythium de baryanum fungus (Cheshunt Compound (cuprammonium solution)
    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 an agent.
    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.
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    Mendel
    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.
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    Acknowledgements
    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 Association http://www.gardenorganic.org.uk

    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 (editors) http://nysaes.cornell.edu/ent

    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 Branch Secretary know.
     
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