Tuesday, 13 September 2016

The Marchantia liverwort.

The tiny Marchantia for me has always had a fascination.  It looks so exotic.   Though the fruiting stems stand less than 4 cms high, they have the appearance of tiny palm trees. The plant has two forms of reproduction.  The 'palm tree' growths carry the sexual organs.  On the wide spreading 'thallus' there are 'gemma cups' easily visible in this photo. These are non-sexual reproductive structures.  The gemmae which develop inside the cups are simply large groups of cells.  They become dislodged with drops or rain and so can be dispersed to grow elsewhere.
The plants are either male or female (dioecious) so that the little palm tree growths carry on the separate plants either the male or the female organs. These called in the male 'antheridia' and the in female 'archegonia' are suspended on the under side of the 'palm like ' 'fronds'.  It is amazing
 to many that the male antheridia produce motile sperm which swim in the raindrops to fertilise the ova in the female archegonia.
After that process has been achieved  tiny capsules grow from the fertilised ova These capsules develop in their interiors tiny spores which eventually may be blown away in the wind to find a new place to grow.
The whole plant carries in every cell nucleus only a half number of chromosomes (haploid). Only the fertilised ovum and the immediate divisions of that ovum have the full double set of chromosomes (diploid).
This photo is of the plant growing in my courtyard, where it can cover a  considerable area.

The Biting Fly Stomomyx calcitrans

 This cursed fly seems to be more common than it used to be.  To the unaided eye it looks like a rather small house fly.  With the aid of a super macro camera one can see more detail. The lower photograph shows the offending proboscis.  It is as hard as horn and can penetrate the soft skin of the human leg with ease, causing much irritation.
It is said that the skin is first cut using the lower lip of the labium and that is certainly how it feels.  The larvae develop in rotting straw or hay especially if it has been used as animal bedding and has been impregnated  with urine.