# Miracle or Physical? Possible Nature of the Burning Bush in Exodus

Anthony D Dayan

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Miracle or Physical?

Possible Nature of the Burning Bush in Exodus

Anthony D Dayan

Garden Fellow, Royal College of Physicians, St Andrews Place, London NW1 4LE, UK

anthony.dayan@rcp.ac.uk

ORCID ID: 0000-0003-3898-6699
**Abstract**

The *Burning Bush that was not Consumed* Exodus 3:1-2 might have been a supernatural
miracle or the underlying idea might have been based on a physical or biological
phenomenon so remarkable that it was taken by the ancient Hebrews as a religious
symbol. The diverse empirical possibilities reviewed here comprise physical
phenomena, such as a volcanic eruption, combustion of escaping natural gases,
electrical phenomena such as ball lightning and earthquake lights, an unusual optical
illusion, or biological processes, such as plants that may appear fiery under particular
circumstances, for example *Dictamnus albus* or a species of Senna.

The most likely rational explanation is considered to be an unusual and little known
optical illusion – the von Linné phenomenon – a flickering effect produced by viewing
appropriately coloured leaves at sunset due to the differential sensitivity of cones and
rods in the retina to changing intensities of coloured light.

**Key Words**

Burning Bush; Exodus; von Linné phenomenon; *Dictamnus albus*
## Introduction

A famed event in the Old Testament (1), repeated in the New Testament (Acts 7:30) and the Qur'an (Surah Al-Qasa 28:29-30), is described in Exodus 3:1-2¹ —

3.1 *Moses was keeping the flock of his father-in-law Jethro, the priest of Midian; he led his flock beyond the wilderness, and came to Horeb, the mountain of God.*

3.2 *There the angel of the Lord appeared to him in a flame of fire out of a bush; he looked, and the bush was blazing, yet it was not consumed.*

Worshippers and a few scientists have long asked whether the idea of the *Burning Bush* that was not consumed was a divine revelation or might an underlying physical event or plant have suggested this remarkable idea. Could there have been something real that was so striking and memorable to the ancient Israelites that it became part of the foundational story of Judaism? In no way would having a natural and not a miraculous origin detract from the supreme religious importance of the event in the life of Moses and the history of Israel, but it could tell us something about the earliest Holy Men and scribes, their circumstances and how a particular event shaped their beliefs.

It is many centuries since the first permanent record of the Old Testament was written down from much older oral and therefore less certain traditions. New ideas about the Burning Bush have subsequently appeared as biblical exegesis and the relevant sciences have advanced. The aim of this brief review is to describe the principal ideas that have been advanced about possible physical or biological origins of the idea of a burning bush that was not consumed.

## Considerations about the Identity of the Burning Bush

If it had been a miracle not explicable by conventional physical or biological means empirical consideration would be futile. However, over the centuries a number of practical possibilities have been suggested as the basis for the features described, which might otherwise seem beyond ordinary human imagination and hint that there could have been some underlying natural event or process with
such a special character that led subsequently to it being adopted into the holy text of the Bible and Qur'an.

Attempts to explain it in empirical terms are inescapably weakened by the lack of a contemporaneous written record as it is only after many centuries of the potentially variable oral tradition from about 3500BCE that we have the earliest written account of Exodus, first in Hebrew (Babylonian Talmud about 539BCE) and then in a subsequent Greek translation (Septuagint from the early to mid-third century CE). The written account we now have is very brief and lacks the sorts of descriptive information required to support confident characterisation of the event, such as clear details of the site of the revelation, of its apparent physical nature or the diagnostic taxonomic features of a plant that might have been the basis of the idea.

Possibilities from the literature discussed below are based on knowledge of the climate and environment at the time of the revelation, generally accepted to be about 3500BCE, evidence of memorable physical events then, of what plants grew or might have grown there at the time and how their features could have been taken as 'Burning without being consumed'.

The extent of the biological and physical speculations is matched by the range of debates about the theological exegesis and spiritual importance of the theophany of the 'Bush that burnt without being consumed'. They are not considered here but there are extensive published accounts2, 3, 4, 5, 6. More magical aspects are briefly discussed in Dennis.7 Baukal8 has provided a detailed review and critique of many of the theological and empirical proposals.

**Where was the Burning Bush Seen?**

Although the site of the revelation has usually been accepted as Mt Sinai or Jebel Musa, more properly called Mt Horeb, in the Sinai peninsula, alternatives have been proposed in the north western area of Saudi Arabia – Ḥalā-ʻl Badr (Mt. Bedr) in north western Saudi Arabia or the nearby Jabal al-Lawz/Jabal Maqla⁹, 10, 11,¹²; Doubting Thomas Research Foundation (https://doubtingthomasresearch.com/jabal-maqla-saudi-arabia/ viewed 10.10.2024).

The local environment at all three sites is of the arid, rocky desert type and rainfall at all the sites is low though possibly less so around Mt Sinai than the others. Accordingly, the natural vegetation is broadly similar. It is sparse and is
dominated by scrub land species, including various *Acacia*, *Astragalus*, *Artemisia* and other xerophytic plants.

## Facts and Clues from Exodus

Moses was leading a flock of his father-in-law's sheep in a rocky, semi-arid area with low rainfall and only sparse scrub species they could eat. It is generally considered that sheep will survive for only a few days to a week without food and for a shorter period if it is hot and they lack adequate pasture.

Although we are not told much about the subsequent fate of the sheep after the vent in question it is likely that they survived because Moses returned to his father in law Jethro (Exodus 4:18) - again a journey of 40 days. There is evidence that the region of Mt Bedr was on a track used by Bedouin for the twice yearly transhumance of sheep flocks from the coastal plains to cooler higher ground in the summer¹¹, ¹², which implies that there would have been sufficient water and food to support sheep in that area.

If these points are accepted the episode of the burning bush was unlikely to have been associated with a contemporaneous active volcanic eruption or major earthquake, as both events would probably have made the area unsuitable for humans or animals, at least for a while. And only if the Burning Bush episode were truly miraculous is it likely that these physical events could have occurred in such a manner that only Moses would have experienced them. These points would make several of the proposed physical basis of the Burning Bush unlikely as discussed below.

## Proposed Causes of the Burning Bush other than a Miraculous Event

### 1. Plants

The many conflicting botanical suggestions with their occasional agreements and more common disagreements are helpfully discussed by Tristram¹³, at greater length by Moldenke and Moldenke¹⁴ and more briefly by the noted expert on local vegetation Zohary¹⁵. There have been two recent lists of plants mentioned in the Bible.¹⁶, ¹⁷ although neither fully explains why they have supported one species over another.

1a. Tristram¹³ concluded that the Burning Bush was *Acacia nilotica* (now *Vachellia nilotica* (L.) P.J.H.Hurter & Mabb.) based on the natural occurrence of that species in the siniatic peninsula, notably on Mt Sinai itself, and also in the
Mt Bedr region, as it grows primarily in a desert and dry shrubland biome. The linguistic relationship of the Hebrew name of the plant סָנָה or seneh, to the Egyptian *sunt* and Arabic *seyal* names for the same shrubby tree are taken as supporting evidence for this attribution. It bears small round balls of yellow flowers, which are sometimes claimed to resemble flames, and that could have made a tree look as if it were on fire. As *Acacia* species bear prominent thorns the absence of any mention of them weakens this possibility.

1b. Moldenke and Moldenke¹⁴ cover the older literature more extensively and critically and give extensive arguments for and against diverse suggestions. They mention *Dictamnus albus* L., popularly called the Gas Plant, Fraxinella or Dittany as well as the Burning Bush Plant (see below for further discussion of this species) because of its spontaneous release of a flammable gas that if ignited can briefly envelop the plant in flames without damaging the leaves.

On the whole they prefer the older suggestion by others that what might have been seen by Moses was the Thorny Acacia or Egyptian mimosa *Acacia nilotica* (now *Vachellia nilotica* (L.) P.J.H.Hurter & Mabb.). It or any of the several related species of Acacia occur naturally in wadis and rocky crevices as are found on Mt Sinai, Mt Bedr and adjacent areas. They could have been regarded as the Burning Bush if naturally infested with Crimson-flowered Mistletoe *Loranthus acaciae* (now *Plicosepalus acaciae* (Zucc.) Wiens & Polhill). It naturally grows in profusion on several species of acacia shrubs and its brilliant red flowers could have given the impression of a shrub or bush on fire without being consumed. Zohary¹⁵ does not accept that *A nilotica* occurs in the Sinai region. As other species of *Acacia* have been recorded in various parts of the Sinai region in different surveys extending over several decades¹³,¹⁸ and as they, too, are susceptible to infestation by *Loranthus acaciae* this remains a valid suggestion.

Like other commentators Moldenke and Moldenke¹⁴ reject the possibility that the Burning Bush was the Holy Bramble *Rubus sanctus* (now *Rubus creticus* Tourn. ex L.) as grown in St Catherine’s Monastery at the foot of Mt Sinai and claimed to be a direct descendant of the Burning Bush.

The monastery was erected in the 6th century CE at a site traditionally believed to have been where Moses saw the Burning Bush. It contains the Chapel of the Burning Bush said to have been built over the site of the roots of the plant seen
by Moses. At the side of that chapel there is a large bush of the bramble held by
the monks to be the Burning Bush.

There are several reasons why that claim is not accepted by expert botanists¹³, ¹⁴, ¹⁵. The species does not occur naturally in the Sinai area and the bush now growing there was only planted by monks in the 13th century. As a typical bramble it is too short lived to have lasted for many centuries. Its leaves are the dark green typical of brambles and become red-yellow only when dying.

1c. Zohary¹⁵, following Haupt¹⁹, strongly advocates Alexandrian senna *Cassia senna* (now *Senna alexandrina* Mill.) as the Burning Bush. He supports this mainly with a linguistic argument based on the similarity of the Hebrew name in the Bible to the Arabic name used today, and the wide natural occurrence of the species in the appropriate areas. It bears racemes of yellow flowers which could perhaps be taken as resembling flames.

1d. Włodarczyk¹⁶ lists *Dictamnus albus* as one of several possibilities but points out, too, that only certain commentators have supported that suggestion. She does not offer a definitive conclusion.

1e. Dafni and Böck¹⁷ are mainly concerned with medicinal plants in the Bible. They do not mention *D. albus*, even though it does have a history of therapeutic use,.

1f. *Dictamnus albus* is a slow growing plant, an aromatic member of the *Rutaceae* family, with dark green leaves and whitish flowers (there are variants) on stems up to 1-1.2 m in height. Oily globules occur in the outer layers of the stems, leaves and roots from which the aromatic ether dictagymnin volatilises and spontaneously decomposes to release the highly inflammable gas isoprene⁸, ²⁰. It occurs naturally in southern Europe, North Africa and much of the Middle East and Asia (21, POWO database, Kew; https://powo.science.kew.org/; viewed 19.10.2024). It grows best in warm, open wooded areas but it can grow naturally in drier rocky areas.

A key question about this species as the Burning Bush is whether it might have occurred in Sinai or NW Arabia, in the areas suggested as the site of the Burning Bush.

It is recorded in Post's *Flora of Syria, Palestina and Sinai*²², repeated in Dinsmore's revision²³, under its former name of *D. fraxinella*. The current Plants
of the World Database maps it now in the same general areas (POWO online; at
https://powo.science.kew.org/; accessed 17.3.2025).

This species is not mentioned in the online *Rare Flowers* database of the *Flora Palestina* of Bethlehem University²⁴, the online *Flora of Israel and Adjacent Areas*²⁵, and in surveys of desert vegetation in Israel and Sinai²⁸ and Arabia ²⁹, Zohary²⁶, in Danin's²⁵ survey of desert vegetation of Israel and Sinai or in Arabia²⁸.

The seeming conflict in these suggestions could be due to geopolitical changes
in the names of several regions in the Middle East. Post recorded *D albus* in
1893 in the region of the Latakia governorate in NW Syria, in woods near Kasak
(Kessab) and Mt Casius, and not in the specific areas of what are now called
Israel and the Sinai peninsula, the areas intensively surveyed in more recent
times.

*Dictamnus albus* has been suggested as the Burning Bush for several centuries
because of its natural production of a vapour from which the flammable gas
isoprene is spontaneously formed³⁰, ³¹, ³ and especially Fleisher and Fleisher²⁰ for
a detailed account of its unique release of isoprene. If it had grown naturally in
the appropriate area (see above) strong sunlight or lightning could have ignited
its emissions. The flames produced envelop the plant superficially and briefly
but do not last long enough to damage its leaves and flowers. The nature and
form of the flames are well shown in videos available on the web; see, for
example, https://www.youtube.com/watch?v=pQTZyS7BKV8; viewed 25
October 2024.

Igniting the isoprene emitted by *D albus* results in a brief and spectacular flame
in the air immediately around the plant. It is external to the leaves and stem and
is short-lived, which together can explain the lack of scorching or other burn
marks on the plant and its continued growth after such a remarkable display of
flammability.

Thus, although the hypothesis that *D albus* could have been the Burning Bush
seems attractive the totality of the evidence and of the major botanical studies of
plants in that area make it less likely without entirely excluding it.

The biblical account states that Moses first saw the ‘Burning Bush’ from a
distance and that it continued to blaze after he left his sheep and walked closer.
As each episode of burning lasts only for a few seconds the requirement for a
repeated source of ignition is a notable weakness in the attribution of *D albus*.
One lengthy and critical review of ideas, speculations and explanations of the
significance of the image and biblical meaning of the burning bush concluded it
could only have been a miraculous event produced by God<sup>8</sup>. In reaching that
opinion many possible physical explanations were discarded as either requiring
circumstances that would not occur in a desert area or being of a type, e.g.
varieties of lightning and other electrical phenomena, volcanic eruptions, natural
gas flames from vents in the earth, for which there is no evidence at the relevant
site, or as being of a type that would anyway have been familiar to Moses, who
had had years of experience of deserts and so would not have regarded it as
something particularly special. As the nature of most such events would have
appeared dangerous or at least threatening it is more likely that an experienced
shepherd would have left the area instead of going closer. We lack information
but such events would be likely to have frightened Moses' flock. Would Moses
as a shepherd have left the sheep in his care just to 'investigate' the phenomenon?
The idea of a plant surrounded by a flame has been denied<sup>8, 11</sup> because it is
considered that the leaves and branches would have been burnt, i.e. consumed.
Against that is the repeated demonstration with *D albus* that it provides short-
lived bursts of flame that are external to the plant and that are too brief to harm
it. Humphreys<sup>11, 12</sup> analogy with a coal-effect gas fire is misleading because that
requires prolonged exposure to burning gas to heat the coals and make them
glow, an entirely different circumstance from brief combustion external to the
plant.

Humphreys<sup>11</sup> explains the biblical description that the 'Bush was not consumed' by suggesting that it was only the carbonized charcoal skeleton of a plant that Moses saw; he notes that *Acacia* species form particularly good quality charcoal when incinerated. But how probable is it that the carbonised skeleton of an Acacia bush, which usually has thin, spindly branches, would have survived the likely force of an hot gas eruption without fragmenting, or that the glowing, ember-like appearance of burning charcoal would have been described as 'The bush that was not consumed'?

Together, although far from definitive, the hypothesis of a carbonised Acacia
bush seems unlikely.
### 1g. Popular but Inadmissible Plants

In popular websites and commercial catalogues there are references to another plant called the ‘Burning Bush’, *Euonymus alatus* (formally *Euonymus alatus* (Thunb.) Siebold) the Winged Spindle Tree, which has spectacularly dense fiery red foliage in the autumn. It bears no relation to the biblical Burning Bush because it is native to North America and would not have occurred in the land of Israel at the relevant time.

A further irrelevant plant sometimes called the Burning Bush is *Kochia scoparia* (now *Bassia scoparia* (L.) Beck), popularly the Burning Bush, Summer Cypress or Mexican Fireweed (https://npgsweb.ars-grin.gov.; viewed 12 September 2024) Its stems turn deep red-purple in the autumn. Although it can grow throughout the temperate biome it is best known as one of the tumble weeds of the Great Plains flatlands just to the east of the Rockies in the USA. It has not been recorded in the Middle East.

### Physical Phenomena

Hypotheses about physical events that might have given rise to the idea of a *Burning Bush that was not consumed* to the ancient Israelites fall under three headings – electrical, geological and optical. Some of these phenomena involve more than one of these classes, e.g. earthquake lights.

#### 2a. Electrical Phenomena

Ball lightning is a rare atmospheric effect that is still not well understood. It presents as a globe of light sometimes up to about a meter in diameter that moves spontaneously through the air and near objects, such as a bush or tree, that it sometimes disrupts or penetrates before ending, often with a bang and a sulphurous smell. It is based on an electrical charge, probably a plasma, but its origin and true nature remain uncertain³³. It is usually associated with storms, thunder and lightning strikes and other, more common electrical phenomena known as St Elmo's Fire ³⁴.

Could some event of this sort have been the source idea for the *Burning Bush*?
The terse description in Exodus 3:2 does not permit a definite answer but it seems unlikely because Moses, having seen the phenomenon from a distance then went closer, implying that what he saw lasted for long enough for him to
pause and then walk an unknown distance to the site of the burning bush, Such a
period would have been very unusual with any of these electrical phenomena.
Also against them is the absence of any mention of the lightning and even thunder
with which they are often associated. The solitary nature of the phenomenon, i.e.
only one burning bush is mentioned, is more like ball lightning than St Elmo's
fire, which is often depicted as forming halos on sharply pointed structures.
Neither of those discharges are said to flicker like ordinary flames.

Whilst the limited description of the *Burning Bush* may not completely exclude
the hypothesis of an electrical discharge phenomenon it does seem relatively
unlikely.

**2b. Earthquake Lights**

The occurrence of short-lived, solitary or multiple, white or coloured lights in the
air or around objects in the ground, including plants, shortly before or coinciding
with earthquakes has long been known.<sup>35, 36, 37</sup> Their origin remains uncertain but
may be due to electrical fields generated by piezoelectric-type effects in certain
types of rocks.

The descriptions of these lights, particularly those arising from the ground and
enveloping terrestrial structures, such as plants<sup>37</sup>, could give the impression of
something burning without being consumed. The absence of an account of those
phenomena from the biblical account could be explained by the fact that they
may occur at the site of earthquakes or some distance away, and before or during
the seismic event. Appropriate types of rock and possible earthquakes and
slippage of rocks along fault lines in the region of Mount Horeb have been
described<sup>11</sup>.

Two arguments against earthquake lights as the source of the idea of the burning
bush are the absence of any direct account of seismic events at the time the
burning bush was seen and the solitary nature of Moses' observation when they
are often multiple.

Neither of those points is a definitive argument against this phenomenon as the
cause of what is described in the Bible but they do make it very unlikely. One
point in its favour that is also applicable to the electrical phenomena discussed
above is that it is not dependent on any particular species of plant

2b. Geological Events
Could what is described in the Bible have been due to a volcanic eruption, the sudden emission of hot gases from a new volcanic vent or even to the escape of natural gas from a channel in the ground? The geology of the likely site of Mount Horeb has been claimed to favour one of these hypotheses<sup>11, 19</sup> as those authors believed there was no realistic physical alternative.

A counter argument as before is that a plant enveloped in hot volcanic gases or burning natural gas would become charred and leaves or branches would be seen to be being consumed.

Moses was able to walk to the bush and to remove his shoes (Exodus 3:5). This would seem unlikely if the ground were being affected by new volcanic events with hot gases or a burning natural gas flare.

Overall, these geological hypotheses seem unlikely.

## 2c. Mount Karkom's Cave

Professor Anati proposed Mt Karkom in the south west Negev desert in the Sinai Peninsula as the site of the Burning Bush.<sup>38</sup> Subsequent exploration there found a cave in part of the mountain which at the winter solstice would briefly transmit the light of the sun as a blazingly bright opening in a rock face (see https://commons.wikimedia.org/wiki/File:The_burning_bush_phenomenon_on_Har_Karkom_as_an_arc_around_the_cave_(14).jpg; viewed 12.09.2024). He and others<sup>39</sup> have suggested that that appearance was the source of the idea of the Burning Bush. Neither that appearance nor Mt Karkom itself have been accepted by other archaeological experts on numerous grounds. Amongst other objections as the opening of the cave is in a precipitous rock face it would not be accessible to a passing shepherd nor would there have been the Holy Ground on which Moses was commanded to stand. And a beam of light from the mouth of a cave does not look like a blazing bush.

## 2d. Optical Phenomena

### von Linné Phenomenon

In 1760 Elisabet von Linné, Carl Linnaeus' second daughter, noticed a strange effect in their garden at Hammarby, Sweden. One day in the later evening, when the sun must have been low on the horizon, she was looking at the orange flowers of Indian Cress (*Tropolaeum majus*; Nasturtium) in the twilight and saw that they appeared to be emitting flashes or sparks of light. Being a keen natural historian
she wrote a paper about it which was published in 1762⁴⁰. This was soon confirmed by others in nasturtiums and later in marigolds (species in the genus *Tagetes*). The effect was so striking that major poets, such as Goethe, Coleridge, Wordsworth and Erasmus Darwin used it in their works⁴¹.

Initially it was considered to be a type of electrical effect although Goethe thought it was somehow being caused in the eye. Subsequent research⁴²,⁴³,⁴⁴ showed it was due to an after-image effect in the eye in low light, as the image was moved across and out of the colour sensitive fovea by the normal scanning motion of the eye. The mechanism is akin to the Green Flash seen immediately after the setting sun sinks below the horizon.

It could explain the Burning Bush phenomenon provided there were enough appropriately coloured leaves in the field of vision, which places particular requirements on the type and form of the appropriate plant, on the angle at which Moses viewed it and on persistence of those requirements for the period over which Moses first noticed it and on the time he took to investigate it more closely. Senescent leaves of most of the species proposed as present on Mt Horeb, such as *Acacia seyal*, *Cassia senna* and *Dictamnus albus*, could meet those requirements. The tighter requirements of a particular angle of sight and the low angle of illumination by the setting sun could also be met under ordinary circumstances. Descriptions of the effect note that the ‘lights’ dance and flicker spontaneously, appearances that could be taken as the ‘blazing’ and ‘burning’ in the biblical description. The von Linné phenomenon is proposed as the likely source of the Burning Bush image not linked to a particular species.

## Conclusions

To the believer the *Burning Bush that was not consumed* has always been a miracle dependent on God not subject to natural laws, and so requiring no further explanation.

The agnostic will wonder if there were a natural event of some sort that at least suggested the idea of the Burning Bush with such striking special properties that it was adopted and subsequently formalised by scribes long after the event as part of the Holy Bible.

In that case, the agnostic and the non-believer alike will ask what was the foundational event, the subject of this review. Can the nature of the event be deduced from very brief textual information and the increasing wealth of detailed
information provided by archaeological and other scientific ideas about the likely
site and its geology, understanding of the climate at the time and, when relevant,
the likely occurrence of identifiable plants?

The published hypotheses, even though most often speculations, have been
divided into physical and biological classes

Physical Events

A number of physical, principally geological and electrical in nature, have been
proposed as explanations for the 'Burning bush that was not consumed'. It is argued
here that none can satisfy the scanty information we have in the Bible.

Biological Explanations

Might there have been a plant that looked burnt but not consumed?

The only species of plant that could realistically be considered as having most of
the required properties is *Dictamnus albus*. Four objections to this suggestion
have been advanced. The species has not been recorded in multiple surveys of
the most likely sites and there is only one unconfirmed report of it in adjacent but
climatically distinct areas, it is usually considered to require a less arid
environment than the hilly and stony sites where the event probably occurred,
and it would only support intermittent burning resulting in brief flashing rather
than the 'burning' in the text, and then only if there were a source of repeated
ignition.

Taken together it seems that it was probably not the species involved.

Several other species have been suggested but there are good arguments against
all of them. Some species would not have occurred naturally at the relevant time
because the soil and the environment would not have allowed them to exist at the
most likely site. Some were not known in the Middle East as they were only
discovered much later in the Americas. Others that did and still do occur naturally
in appropriate sites, particularly species of *Acacia*, even if carrying a red
mistletoe, would surely have been recognised as a common finding by Moses as
an experienced shepherd and he would most probably not have gone closer to
investigate it.

Combining two particular factors does suggest a novel possibility. Could Moses
have observed yellowing leaves on an appropriate species common in the arid
area through which he was guiding his flock, such as *Acacia seyal* (now
*Vachellia seyal* (Delile) P.J.H.Hurter), and under circumstances where the von Linné optical phenomenon gave the appearance of flickering yellow lights? They could have given the impression of a burning bush that was not being consumed. This idea demands quite specific conditions before the phenomenon would have been observed but they are not impossible, such as the setting sun and the angle at which the observer views the plant. The latter would have required Moses to have had the same angle of view when he first saw the bush and after he had walked nearer to get a closer look and neither seems impossible.

To conclude, the biblical description of Moses observing a *'Burning Bush that was not consumed'* could have been a miracle, a supernatural event. Or, if the concept were based on a real world event, it is proposed that it was that it would have been an unusual optical illusion, the von Linné phenomenon, giving an unusual perception of a desert plant under a particular set of conditions.

**Acknowledgements**

I am grateful to Dr E. Hesse for translations of the German publications.
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