Question: Can you define Flagella?
About the article "Bacteria", section "Movement".

Candidate passages:
s in vascular plants.
Zoids are found in three types of vascular plants; ferns, cycads, and "Ginkgo biloba".
The zoids of each of these groups are large and multi-flagellated.
The mature spermatozoids of the fern "Asplenium onopteris" are 8 to 8.5 micrometers in length and contain 50 flagella.
The zoid of the cycad can be up to 300 to 500 micrometers long and can contain thousands of flagella.
The zoid of the ginkgo is approximately 86 micrometers long and also can contain thousands of flagella.
Because of the high number of flagella associated with both cycads and ginkgo, there has been some debate as to whether they are flagella or cilia.
Either way, cycads and "Ginkgo" are rare woody plants that produce motile gametes. 
In the Ruby language you can use multiple ways to simulate this function, for example:Or you can define your own method: 
Three types of flagella have so far been distinguished; bacterial, archaeal and eukaryotic.
The main differences among these three types are summarized below:  Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise.
They provide two of several kinds of bacterial motility.
Archaeal flagella (Archaella) are superficially similar to bacterial flagella, but are different in many details and considered non-homologous.
Eukaryotic flagella - those of animal, plant, and protist cells - are complex cellular projections that lash back and forth.
Eukaryotic flagella are classed along with eukaryotic "motile" cilia as "undulipodia" to emphasize their distinctive wavy appendage role in cellular function or motility.
"Primary" cilia are immotile, and are not undulipodia; they have a structurally different "9+0 axoneme" rather than the "9+2 axoneme" found in both flagella and motile cilia undulipodia.  
"Oedogonium" can reproduce asexually by fragmentation of the filaments, through some other types of non-motile spores, and also through zoospores, which have many flagella.
These develop in a zoosporangium cell, one zoospore per zoosporangium.
After settling and losing its flagella, a zoospore grows into a filament. 
Most archaea (but not "Thermoplasma" and "Ferroplasma") possess a cell wall.
In most archaea the wall is assembled from surface-layer proteins, which form an S-layer.
An S-layer is a rigid array of protein molecules that cover the outside of the cell (like chain mail).
This layer provides both chemical and physical protection, and can prevent macromolecules from contacting the cell membrane.
Unlike bacteria, archaea lack peptidoglycan in their cell walls.
Methanobacteriales do have cell walls containing pseudopeptidoglycan, which resembles eubacterial peptidoglycan in morphology, function, and physical structure, but pseudopeptidoglycan is distinct in chemical structure; it lacks D-amino acids and N-acetylmuramic acid.
Archaea flagella operate like bacterial flagella—their long stalks are driven by rotatory motors at the base.
These motors are powered by the proton gradient across the membrane.
However, archaeal flagella are notably different in composition and development.
The two types of flagella evolved from different ancestors.
The bacterial flagellum shares a common ancestor with the type III secretion system, while archaeal flagella appear to have evolved from bacterial type IV pili.
In contrast to the bacterial flagellum, which is hollow and is assembled by subunits moving up the central pore to the tip of the flagella, archaeal flagella are synthesized by adding subunits at the base.