Plant bile

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Gall apple on an oak

A plant gall or cecidia , also called gall apple , is a spherical swelling on plants (from Latin galla , "swelling on plants and animals", in particular denoting the oak bile caused by the sting of gall wasps on oak leaves ) an anomaly in plant growth caused by foreign organisms caused. The science of plant galls ( cecidia ) is also known as cecidology .

A generally accepted definition of the term plant bile does not yet exist. Various attempts have already been made to comprehensively describe the formation of gall on plants. The definition by Ernst Küster from 1953, which is also frequently used in current literature, defined plant galls as “products of abnormal growth” that “arise through the action of animal or plant parasites and provide the breeding ground for them”.

But nowadays there are many other definitions that describe the phenomenon of gall formation. Due to the large variety of gall pathogens, however, a clear definition is difficult, as some types of gall, such as stunted formation of individual organs, are not mentioned in most definitions.

History of Cecidology

While the economic benefits of some Gallen man had been known, some galls on oak served as for the production of iron gall ink and as a tanning agent in the tanning , the scientific study of this discipline began biology towards the end of the 17th century. The first scientific description of the phenomenon of gall formation in plants can be attributed to Hippocrates of Kos , who considered the observed growths only for special fruits of the plants and recognized no connection between parasites and gall formation.

It was Marcello Malpighi who initiated the breakthrough in cecidology with his book Anatome Plantarum idea . There he described 60 different gall forms in detail in the De Gallis chapter and tried to systematize and define the phenomenon of gall formation for the first time.

Living organisms producing plant galls

Describing the organisms that cause gall formation is simpler than the definition of a plant bile. In principle, the gall producers come from almost the entire spectrum of living things. However, they are caused in particular by viruses , bacteria , fungi , mites and insects . The majority of the gall-producing species are made up of insects. A total of almost 15,000 species are known from the entire spectrum of living beings that are capable of forming gall on plants.

Gall pathogens and infested plants do not always live in a parasitic relationship that causes damage to the plant. Apart from a few species such as phylloxera , which causes massive damage to host plants, most gall producers interfere with the metabolism of their host in a hardly measurable way. There are even symbiotic relationships between some plants and the gall producers on or in them. This subheading includes the root nodules of the butterfly family .

The gall wasps are among the best-known bile-producing creatures, which draw attention to themselves with their often large, strikingly colored and shaped structures, which can usually be seen on oak leaves. The undoubtedly largest galls in plants are caused by fungi, such as the fruit tree cancer . Some pathogens also stand out due to their unusual way of life, such as the aphid species Pemphigus spirothecae , in whose generation cycle soldier lice occur, which as a caste do not reproduce and instead defend the bile population against invading enemies. This fulfills one of the conditions for eusociality .

Many of the more highly developed gall producers show a generation cycle that repeats itself over the course of one or more years and during which asexual as well as sexual reproduction takes place. Often a generation change goes hand in hand with a change of host or of the host's habitat.

Formation of a plant bile

The exact origin of a plant bile varies greatly from species to species. While the presence and multiplication of the parasite in the plant organs alone leads to the externally visible deformations, especially in lower forms of life , more highly developed organisms have developed methods with which they specifically intervene in the growth of the plant parts. The spectrum of changes in the plant ranges from the targeted inducing of abnormal growth to the formation of completely new organs that develop out of the existing organs of the plant.

Especially in the field of insects and arachnids, the animals often create closed and non-closed cavities around them as a result of their growth, in which they have protection from weather conditions and predators.

The development of bile is caused and controlled by insects by injecting so-called cytokinins into the plant tissue to be modified, which creates the shapes characteristic of the bile. The more highly developed gall producers in particular use cytokinins to form the galls. These cytokinins can trigger growth-inhibiting, growth-increasing and generally regenerative processes in the gall tissue.

Gall development is rarely exactly the same. In fact, the treasure trove of forms that can be produced by a single species is sometimes so great that the galls have often been assigned to different producers.

Classification of the different gall forms

Basically, gall structures can be classified into histoids and organoid galls . However, many galls cannot be clearly assigned and have different properties from both the histoid and the organoid galls .

Organoid galls

Branching anomaly (" witch's broom ").
Gall formation of the gall mite Aceria genistae on the leaves of the broom .

Organoid galls are modifications in the formation of individual organs in plants and can be further subdivided into form anomalies , leaf position anomalies , branching anomalies and new organs.

Histoid galls

Histoid galls are changes in plant tissue that cannot be broken down into individual organs. You can in Filzgallen , Blattrollungen , leaf folds , bags Gallen , Umwallungsgallen and Mark Gallen are divided.

Felt galls

In felt galls, a small layer of hair called felt forms on the plant's epidermis . This is inhabited by the gall pathogens, mostly gall mites . The hair layer serves as protection against bad environmental conditions and predators.

The galls of Aceria genistae on broom are easy to find .

Leaf curls and folds

Leaf folding caused by the gall mosquito Macrodiplosis dryobia
Pouch gall at the top of a gold elm leaf

Plant galls, which are caused by leaf curling or leaf folding, change the natural leaf growth at a kink where the leaf end begins to roll up and form a protective layer around the pathogen. Galls caused by leaf curling or leaf folding are caused by faster growth on the lower side of the leaf or by an inhibition of growth on the upper side of the leaf. This change creates both a typical kink and an oval-shaped fold on the upper side, which wraps around the pathogen like a protective armor. This layer formed in this way protects it against adverse environmental influences and predators, but is usually easy to open, since the end of the roll usually does not grow together with the upper side of the leaf, but just rests on it.

Pouch galls

Pouch galls are created by the elongation of all leaf tissue layers , which leads to a protuberance at the point of attack of the pathogen. This elongation leads to the formation of a large cavity which is inhabited by the pathogen. Only a small opening on the underside of the sheet often remains, which is often closed by a fine layer of felt and thus allows air to be exchanged.

Walling galls

Walling galls are created when the pathogen triggers a strengthened bead-like growth around itself on the leaf surface , which eventually grows together over it and traps the pathogen. Often, however, a small exit hole remains through which the pathogen can leave the bile as soon as its development is complete.

Marrow galls

Marrow galls are gall forms in which the growth of the bile originates from the inner layers of the plants. They can be divided into closed galls and free galls .

  • With closed galls, the tissue of the plant is not broken to the outside. The growth reaction is limited to the inner tissue.
  • Free galls, on the other hand, penetrate the tissue layers of the host organ.

Division of the gall tissue

Tissue resulting from gall formation can be divided into cataplasmic and prosoplasmic gall tissue.

  • In cataplasmic tissue, the tissue structure of the affected organs is the same or very similar to that of unaffected juvenile organs of the same type.
  • Prosoplasmic tissue shows differentiations that do not occur in normally developed tissue of the plant organ.

Determination of galls

Andricus quercuscalicis on Quercus robur
Cecidia on Schinus polygama

In view of the large number of bile pathogens, an unambiguous determination of the bile pathogen is not always easy. The most important characteristic of a gall pathogen is the host on which it develops its bile. However, it must be taken into account here that some gall pathogens change host.

One of the most popular hosts is the oak , on which many species in particular develop their galls. Why so many gall pathogens have specialized in oak has not yet been researched.

Another important criterion is the exact location of the formation of the bile on the host. In principle, all organs of the plant can develop galls, whereby the parts of the plant that are above the ground have a significantly higher number of bile pathogens that specialize in them. In addition to the leaf gall , which can be found quite often and which are formed on the leaves of the host plant, the organs of the plants most frequently affected are the flower , the root and the stem or stem of the plant. In addition, there are also pathogens that can change the growth of the entire plant, at least the above-ground part.

Another distinguishing feature is the temporal appearance of the bile on its host. However, it must be taken into account here that the occurrence of numerous forms of gall, in particular caused by bacteria, viruses and other single-celled organisms, is not limited in time.

A division into properties of the bile has already been proposed by some researchers, but no system for classification has been able to prevail to this day. Such a categorization is also made more difficult by the fact that galls usually have several shaping properties. This is further complicated by the fact that even gall formations of a gall pathogen that take place on the same plant organ can differ significantly from one another, both in terms of their overall shape and tissue structure. In addition, external circumstances such as the condition of the host plant and general climatic and meteorological circumstances can strongly influence the structure and growth process of the bile.

The abandoned bile

Abandoned galls often serve as a refuge for equilines , which move into the bile after the bile generator has already left the bile, or remove or eat the bile generator from the bile. In some cases, the presence of the equilines changes the shape of the occupied bile so that one can distinguish them from the outside from unoccupied bile and galls that are still inhabited by their original producers.

In addition to equilines, there are also some secondary and tertiary parasites that can also be found in the galls. The presence of these parasites is often associated with the death of the gall producer.


Individual evidence

  1. See for example Jürgen Martin: The 'Ulmer Wundarznei'. Introduction - Text - Glossary on a monument to German specialist prose from the 15th century. Königshausen & Neumann, Würzburg 1991 (= Würzburg medical-historical research. Volume 52), ISBN 3-88479-801-4 (also medical dissertation Würzburg 1990), p. 129 ( galla ).
  2. Plant Galls and Cecidology: What are Plant Galls ?
  3. ^ Rolf Beiderbeck, Ingo Koevoet: Plant galls on the wayside. Origin and destination. ISBN 3-440-04751-2 .


German speaking
  • Heiko Bellmann : bees, wasps, ants. Hymenoptera of Central Europe . Kosmos (Franckh-Kosmos), 2005, ISBN 3-440-09690-4 .
  • Ernst Küster : The galls of plants . Leipzig 1911.
  • Rolf Beiderbeck & Ingo Koevoet: Plant galls by the wayside - origin and purpose . Kosmos Verlag, 1979, ISBN 3-440-04751-2 .
  • Herbert Buhr : Determination tables of the galls (zoo and phytocecidia) in plants of Central and Northern Europe. Gustav Fischer Verlag, Jena 1964/65.
  • G. Hieronymus: Contributions to the knowledge of the European zoocecidia and the distribution of the same . Gross, Barth & Co., Breslau 1890.
  • Karl Czech: New division of the plant galls . Gross, Barth & Co., Düsseldorf 1858, urn : nbn: de: hbz: 061: 1-115216 .
English speaking
  • Ron Russo: Field Guide to Plant Galls of California and Other Western States . University of California Press, London 2006, ISBN 0-520-24886-4 .
  • Arnold Darlington: The Pocket Encyclopaedia Of Plant Galls In Color . Blandford Press, Dorset 1968, ISBN 0-7137-0471-3 .
  • Margaret Redfern, Peter Shirley: British plant galls: Identification of galls on plants and fungi . Field Studies Council, Shropshire 2002, ISBN 1-85153-214-5 .

Web links

Commons : Plant Galls  - collection of images, videos and audio files