Phyllotaxis

The phyllotaxis ( from ancient Greek φύλλον phyllon, leaf ' and Greek ταξις taxis, arrangement ') is the study of the leaf position of plants.

Leaves are not randomly arranged on the stem, but their arrangement follows certain rules. Although Leonardo da Vinci had already noted in his diaries on this fact, the botanist Karl Friedrich Schimper is considered as the one that gave rise to the underlying mathematical laws. Through his work, a separate subject area was founded in 1830, namely the doctrine of the leaf position ( or from the Leaf ), foreign language phyllotaxis. Several still used technical terms - such divergence, ring, ortho and para stitches stitches ( see "Design" ) - were marked by Schimper. Alexander Braun, who was also a pioneer in the field, was inspired by Schimper in his research.

Because von Braun's discoveries is often spoken of the Schimper - Braun leaf position teaching.

• 2.1 Basic and spiral divergence
• 2.2 worksheet rows ( Ortho stitches ) and cycle
• 2.3 Para stitches

Basic types

Constantly changing

Here, the leaves are individually along the stem axis, that is, none is linked to another on the same level. Most are opposite leaves:

• Schraubig (dispersible )

Or

• Two lines ( distich )

Opposite

The leaves are in pairs, and indeed against, along the stem axis. Mostly then enters the following case:

• Decussate ( dekussiv )

Whorl or whorls

When whorl or whorled basic type spring on the shoot more than two leaves at the same height.

Rosettes

Due to reduced growth in length of the stem, it may happen that many leaves sitting on approximately the same height. One speaks in this case of a rosette of leaves. Frequently there is a rosette of leaves on the stem end. What is even more common following case:

• Basal

Construction

Basic spiral and divergence

When thinking of a stem with alternate leaves so from the bottom progresses upward so that all the leaves as they follow each other upward touching, so it describes a stem umwindende the spiral line, the so-called basic spiral.

This results in the characteristic, that the piece of the stem periphery, which one has to rotate with the spiral, to move from one disc to another, wherein all sheets of the stem is the same. This elbow is called divergence ( the leaves); they can be expressed in fractions of the stem periphery, ie as a number between 0 and 1

Sheet lines ( Ortho stitches ) and cycle

In some plants these fractions rational ( breakage ) of the peripheral parts, it follows that each time a sheet is just above the output sheet after a certain number of sheets. As one ascends at a leaf position with a divergence of 2/ 5 in the spiral of sheet 1, then sheet 6 is the first one that is again perpendicular to the output sheet. Also available is sheet 7 on Sheet 2, Sheet 8 on sheet 3, etc. It can be so in these cases, the leaves, the side sitting on a stem, connected by a series of straight lines that are called leaf rows ( Ortho stitches ). You can see the leaf position therefore also be described as two-line, three-line, five-line, and so on.

The part of the basic spiral, you have to cover in order to move from one gate leaf until the next vertical sheet above it, is called cycle (obsolete: cycle ).

Para stitches

In whorled leaves the individual members of the whorl group at equal intervals around the stem. If successive whorls, are usually the leaves of the whorl next above the center of the gaps between those of the preceding; that is, the first and third whorl are mutually equal, what is called Para stitches.

Golden section

In plants, it has been found that primitive species have a divergence (angle between three successive sheets of the basic spiral, see figure ), which corresponds to the golden section.

There are two main theories why this is so in plants:

• The leaves take up much space and displace other species
• The sugar solution, which is produced by photosynthesis is uniformly distributed on almost all vascular bundles of the phloem, as the leaves open exactly on top of another in the branch.

Control over hormones

The primary growth of the plant takes place in the apical meristem instead (so-called Apex, also bud ). The apex rotates during growth around its own axis; this leaf primordia are always formed, ie leaf primordia, where later form the leaves.

The hormone auxin is transported from the apex to the blade system down. The Auxinabsorption by the primordia already existing directing the position of the new primordium. Auxin is absorbed by the existing primordia and thus removed from the nearby area ( lateral reduction). The new primordium can not be built next to the old sheet plant, since an accumulation of auxin can only begin at a certain minimum distance. Because the youngest leaf plant auxin absorbed more strongly than the second youngest, the new primordium arises closer to the second youngest as the youngest primordium. This is the reason why the divergence angle between two successive primordia formed a typical angle of 137.5 ° ( " Golden Section " ) corresponds.

Petals

As petals are special developments of the normal leaves, one finds the basic arrangements of phyllotaxis, sometimes with adhesions of the single sheets, even when the flowers themselves, and in the inflorescences.