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Below you can see:

- schemes of the ovule development

-short movie scene showing two motile sperms + snapshots + YouTube video and more



 
ovules with pollination droplet (photo Cor Kwant)
 pollination droplet is present on the micropyle 
at the tip of the integument

 
Ovule development

Ovule developmentgametophyte
 
 

immature seedmature seed
immature (left) and mature (right) enlarged, fleshy seed with inner hard part (black)
Drawings adapted from Fig. 22-15 in Bold, H. C. et al. (1987), Morphology of plants and fungi, 5th ed. New York, Harper & Row. 

Drawings courtesy University of Toronto (Canada).

Ginkgo embryo
young embryo
Ginkgo female ovuliferous structures
 female ovuliferous structures

images University of Lethbridge, Alberta, Canada


ovule

Drawing after 'Pour la Science' 2008.

pollen
 microstrobilus

Ginkgo pollen

images University of Lethbridge, Alberta, Canada


motile sperms in the pollen chamber

During the months following pollination, the pollen grows big enough to form two motile sperms in the pollen chamber.


Click here to see a short film scene (2.2 MB) showing two motile Ginkgo sperms.

Scene from the research film 'The sea in the seed, sperm of Ginkgo biloba and reproductive evolution  in plants' , produced by Okada Kazuo; the best scientific film award at Ronda, Spain and TEPIA Grand Prix in Tokyo (2000) -  TokyoCinema Inc.

Film Sea in the Seed

Some snapshots from this film :
pollen
pollen grains
Ginkgo pollen grain
Ginkgo ovules
Spring: the pollen on the male Ginkgo tree are growing. The pollen grains are released from the pollen sacs of male trees (April-May); they are carried to the female trees by the wind. The pollen grain is four-celled. One of the cells produces sperms. A pollen grain is therefore a "flying gametophyte". On the tip of a young ovule is a pore through which the pollen enters.
pollination droplet
droplet with pollen
archegonia
pollen chamber
When it is ready for pollination a droplet is released from the inside of  the ovule to catch the pollen. Repeatedly the drop retracts in the tiny opening and brings the pollen grains into the pollen chamber. Fertilization does not occur immediately after pollination. 
The  actual fertilization mostly takes place in fall (depending on external temperature). Inside the archegonia egg cells are maturing. 
Usually only one of the two fertilized eggs germinates. During the months following pollination, the pollen forms two sperms in the pollen chamber, absorbing water and fertilizer from the female tissue - a nucellus. 
sea in seed
Ginkgo sperms
swimming Ginkgo sperm
Ginkgo sperm
The pollen chamber and the space around the tentpole unite into a bigger archegonial chamber. This fluid could be regarded as "the sea"  in the seed. Two sperms in the pollen tube.  The pollen tube ruptures and the Ginkgo sperms swim upwards in "the sea" toward the eggs. The Ginkgo sperm has c. 1000 flagella (cilia) arranged in a spiral.  The sperm of the Ginkgo has many similarities with that of the Cycad.
The Cycad and Ginkgo have partially followed the same reproduction method the ancestors of green plants had in the water; they produce a similar watery environment in a seed. 
swimming Ginkgo sperm
fertilization
Ginkgo seed
More info on my Propagation-page.
Videos I made of pollen / seeds:
click here.

More photos of the seed development here.

Ginkgo sperms swim forward with cilia at the front. Compared to mosses and ferns, Ginkgo sperm can swim safely in this "inner sea" and can reach the egg cells more successfully. The sperms swim shortly in the liquid. The egg cells attract nearby sperms to the entrance of the archegonium, then one of them fuses with the egg nucleus, the actual fertilization. 
Ginkgo biloba and the cycads are the only living seed plants with motile sperm cells.
.germinating Ginkgo seed
.Ginkgo seedling
Film scene © TokyoCinema Inc.
Snapshots taken from this film and other photos: Cor Kwant.

 To watch the full movie "The sea in the seed": click here.

The spermatozoid of Ginkgo biloba
Video on YouTube about the spermatozoid of Ginkgo biloba, first discovered in seeds obtained by Sakugoro Hirase in 1896. More on this video: Cycas revoluta and Slime mould.
From ScienceNet, Japan

Video Ginkgo spermatozoid

Video fragment: spermatozoid of Ginkgo biloba
(This fragment is not on YouTube; loading please wait.)
From ScienceNet, Japan


Videos I made of trees / pollen / seeds: click here.

Watch video (Japanese): Swimming Ginkgo sperm (includes micro fragments): click here.
 
 
 

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