BioelectricaAlterspan Labs
Morphogenesis and form  ·  Article

Polarity

Polarity is an asymmetric distribution of a property along a body axis, such as head versus tail or apical versus basal. It persists in cut fragments and in single cells. Authors from Vochting to Levin have asked what sets and keeps it: the tissue itself, a chemical gradient, nerve direction or a voltage pattern.

Earliest held
1880, Darwin, C.
Most discussed in
Physiological Foundations of Behavior, 1924
In the library
1,011 passages in 81 works
Rewritten
2026-10-03
18501875190019251950197520002025Morgan, T. H., 19011Morgan, T. H., 19012Bayliss, W. M., 19153Child, C. M., 19154Loeb, J., 19165Child, C. M., 19246Lobo D, Beane WS, Levin M, 20127Pietak A, Bischof J, LaPalme J…, 20198Levin M, 20259
01

Polarity in cut pieces

Morgan (1901) reported Vochting's grafting work on plant pieces. Pieces grafted in their original orientation united perfectly, while reversed pieces joined incompletely or later died.1 Vochting claimed that every part has a polar orientation. He held that each living cell of the root is polarized along its length and also radially.1 In short internodal stem pieces, leaf-buds appeared at the apical end even when that end pointed down. Vochting concluded that these pieces show the same polarity as longer ones.2 A ring cut through the cambium made the parts above and below act as separate pieces.2

02

Gradients and chemical control

Bayliss (1915) described Errera's work on pines. Errera suggested that the apical bud forms an internal secretion that stops lateral shoots growing upward while the bud is present.3 Loeb (1916) worked with leafy stem pieces. He found that leaves speed root growth toward the basal end and inhibit it toward the apical end.4 Child (1915) argued that double apical regions in pieces are not abnormal. He said they follow the same laws as a normal individual, and that raised activity at the basal end may set up a new gradient in the reverse direction.5 Child (1924) added that in very short pieces polarity may follow contact with the substratum, independent of the original polarity.6

03

Planarian fragments

Lobo, Beane and Levin (2012) describe planarian polarity as most prominent along the head-tail and dorsal-ventral axes. A trunk fragment with head and tail removed always regrows its head in the original orientation, even without the brain and pharynx.7 Pietak and colleagues (2019) set two hypotheses against each other: control by pre-existing morphogen gradients, or by the direction of net innervation. Small fragments without the ventral nerve cord regenerated an axis rotated by 90 degrees. The authors took this to mean that average axon polarity is the dominant driver.8 Fragments with the cord keep the original axis because its large nerves dominate transport.8

04

Bioelectric prepattern

Levin (2025) places the polarity of the planarian head-tail axis among organ-building cascades tied to voltage states. He states that altering the bioelectric pattern for a few hours can convert regenerating worms to a two-headed form.9 He reports that the two-headed state is permanent and persists without further manipulation.9 He argues that this is not reflected in any genetic change and calls it non-genetic inheritance of morphology.9 Pietak and colleagues' result on nerve direction gives a second, separate account of what fixes the axis in fragments.8

SourcesEach quotation was checked word for word against the passage it opens.
  1. every living cell of the root is polarized, not only longitudinally, but also radially ; each has a different apical and root poleMorgan, T. H., 1901 · Regeneration · open at passage 455
  2. Vochting concludes that the same polarity that is a characteristic feature of longer pieces is also present in internodal pieces.Morgan, T. H., 1901 · Regeneration · open at passage 185
  3. He suggested that the apical bud of the main stem forms some kind of an internal secretion, which prevents the upward growth of the lateral shoots as long as this apical bud is present.Bayliss, W. M., 1915 · Principles of General Physiology · open at passage 2998
  4. the original gradient is almost absent, and the increased activity at the basal end may establish a new gradient in the reverse directionChild, C. M., 1915 · Individuality in Organisms · open at passage 169
  5. the leaves accelerate the growth of roots towards the basal end and inhibit it towards the apical endLoeb, J., 1916 · The Organism as a Whole, from a Physicochemical Viewpoint · open at passage 266
  6. In very short pieces this determination of polarity in relation to the substratum and the differential exposure of the pieces may be quite independent of the original polarityChild, C. M., 1924 · Physiological Foundations of Behavior · open at passage 318
  7. a worm trunk fragment generated by removing both the head and tail will always re-grow its head in the same orientation as the original wormLobo D, Beane WS, Levin M, 2012 · Modeling planarian regeneration: a primer for reverse-engineering the worm · open at passage 23
  8. average neural axon polarity in a fragment is the dominant driver of anatomical polarity via the directional transport of morphogens with respect to nerve polarityPietak A, Bischof J, LaPalme J, Morokuma J, Levin M, 2019 · Neural control of body-plan axis in regenerating planaria · open at passage 61
  9. Altering the bioelectric pattern for just a few hours can convert regenerating planaria into aLevin M, 2025 · The Multiscale Wisdom of the Body: Collective Intelligence as a Tractable… · open at passage 44
Linked ideas
Child explains polarity and double-headed pieces through an axial gradient; Pietak et al. test gradients against nerve direction as the source of polarity.
Regenerationpart of / contains
Polarity decides which end regrows a head or tail in fragments, as in Vochting's plant pieces and planarian trunks.
Emmons-Bell et al. say voltage gradients regulate positional information and axial polarity.
Resting-potential gradients across cell types are named as instructive cues for axial polarity.
Pietak et al. model morphogen gradients whose transport direction sets the regenerated anterior-posterior axis.
Lobo et al. link left-right to dorso-ventral axes in vertebrates and describe medial-lateral polarity in planarians; Carneiro et al. note the left-right axis is oriented relative to other axes.
Child holds that cells' environment, not heredity alone, sets which body region they form; Durant et al. link neurotransmitters to polarity.
Tropismrelated to
Driesch's negative geotropism of the main axis, taken over by a side branch, ties a directed response to the organism's axis.
In planarians, praziquantel-induced bipolar phenotypes are rescued by exogenous serotonin, tying neurotransmitter signalling to polarity.
Child argues something must determine why cells with identical nuclei form a head at one axial end; Bose seeks the conditions that predispose or reverse polar effects. Polarity is treated as condition-determined.
Galvanotaxisrelated to
Child ties galvanotactic orientation to the axial gradient: the high end faces the negative pole. Funk links cell polarity (front-rear pH gradient, NHE3) to electrotaxis. Lillie sees current direction determining polar action.
Vmem depolarization patterns are tied to body axes: a depolarized A/P boundary stripe in Drosophila wing discs, ivermectin depolarization promoting head regeneration in planarian and Macrostomum fragments. Electrical 'polarization' otherwise is a separate sens
Gap junctionsrelated to
Blocking gap junctions in planaria gives secondary heads, so junction communication is needed for head-tail polarity.
The thinner ectoplasmic wall on the lower side of a slime mould tube was described as morphological geopolarity.
Passages link them causally: asymmetric ion channel and pump distribution, from the egg onward, creates asymmetric ion gradients and Vmem patterns that drive left-right and A/P axis patterning; epithelial apical/basolateral domains differ.
Bose treats 'polar effects' of electric current as a feature of excitation shared by plant and nerve; the organoid passage uses polarity as cell asymmetry in budding, a different sense. Link is partial.
Where it is discussedPassages matching polarity, anterior-posterior, head-tail, apical
1924Physiological Foundations of Behavior · Child, C. M.184
1915Individuality in Organisms · Child, C. M.120
1901Regeneration · Morgan, T. H.72
1906Plant Response as a Means of Physiological Investigation · Bose, J. C.70
1992On Growth and Form · Thompson, D. A. W.65
1923Protoplasmic Action and Nervous Action · Lillie, R. S.62
1894Materials for the Study of Variation Treated with Especial Regard to… · Bateson, W.41
2019Neural control of body-plan axis in regenerating planaria · Pietak A, Bischof J, LaPalme J…32
1899General Physiology: An Outline of the Science of Life · Verworn, M.30
2016Bioelectric modulation of macrophage polarization · Li C, Levin M, Kaplan DL26