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Hidden sex life of ferns     
In samenspraak met Phil Gates, een botanicus aan de Durham Universiteit - de derde universiteit van Engeland - mag de Nederlandse Varenvereniging een deel van zín gevonden ímicro-varen-schattení op
haar website publiceren. Wij zijn hem daarvoor zeer erkentelijk.

The hidden sex lives of ferns, tekst en fotografie,  Phil Gates [Botanist, Durham University, UK]

 

Fern spores are produced in vast numbers on the underside
of fern fronds during the summer months.

Each spore is less than a hundredth of a millimetre in diameter
and can be carried vast distances on air currents.
Ferns are often the first plants to colonise bare volcanic
lava flows, carried there as spores on the wind.

All they need for germination is water and mineral salts.
They swell, the brown spore case splits open and a hair-like
rhizoid emerges, that anchors the spore to its substrate.
Then a green photosynthetic cell emerges from the spore.

The photosynthetic cell divides longitudinally, forming
the beginnings of a short chain of cells.
The green blobs in the cells are chloroplasts.

The chain of cells continues to elongate until it reaches 6 - 7 cells
long, dividing longitudinally and producing more rhizoids to
anchor itself more firmly. At this stage the remains of the
brown spore coat is still visible. During this stage of development
the plant must be constantly wet, even a short period of drought
will be fatal.
I sowed these spores in September, so they've taken about
four months to reach this stage, where they appear to the
naked eye as a green film covering wet soil.

This is the next crucial stage in development and is about a
millimetre long. The tip cell of the thread now begins to divide
laterally and longitudinally, forming a flat plate of cells...

Here you can see this two-dimensional tip division at higher
magnification. The flat plate of cells that develops from
this is known as the prothallus, and this is where
fern sexual reproduction takes place ...

These are two fully developed prothalli, each about 5 mm.
in diameter and only one cell thick. They are incredibly
delicate and must remain permanently wet to survive.
At this stage they are about six months old and male
and female reproductive cells form on their surface.

These are the male antherozoids, enclosed in a structure called the
antheridium. When this bursts the antherozoids are released in
swarms and swim, propelled by lashing flagellae, like tiny
spinning tops in the surface film of water, in search of a
female egg cell inside a long-necked structure called an
archegonium, which you can see here.After a successful
fertilisation an embryo develops which ultimately grows into a ...

... New miniature fern plant. In the early stages, as seen here,
itís still attached to the prothallus formed by the germinated
spore but that soon withers away and the new fern grows
by producing a series of ever-larger fronds.
It usually takes about a year after sowing to reach this stage.

Provided you have the required patience, ferns are not difficult to grow from spores.

Met toestemming van Phil Gates overgenomen van zijn blog BEYOND THE HUMAN EYE
Microfotografie van planten en insecten, o.a. Polypodyum, fern with golden sporangia

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