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A walk through time

Volume 5 Number 2 - October 2008
Mara Sugni

French title: Une promenade à travers le temps

Spanish title: Un paseo a través del tiempo

Summary

Visitors in Italy have been invited to take a walk back in time through the evolution of plants at Bergamo Botanic Garden. As part of their celebrations of Darwin’s 199th birthday, the gardens have created an exhibition focussed on the adaptive strategies of plant movements. Strategies such as tropisms to light or touch have been extremely important in the evolutionary development of plants and Darwin in his latter years did extensive work on both. This work was revolutionary for botany as well as helping to solidify his evolutionary theory. The exhibition has used lower plants such as algae through to higher plants such as trees to highlight the importance of tropisms to plant evolution. Practical activities are offered and there is an opportunity for visitors to interact with botanists and take a refreshing drink in the garden’s ancient Sala Viscontea laboratory rooms.

A special birthday party was held this year on 12 February at Bergamo Botanic Garden, Italy, to celebrate Charles Darwin’s 199th birthday. In a crowded medieval laboratory room (Sala Viscontea), where educational activities usually take place, visitors were offered a unique presentation about Darwin’s work concerning plant sensitivity and movement.

The evening party began with Darwin’s words spoken by an actor, located in a scene resembling Darwin’s studio. The actor read some extracts from the texts The Power of Movement in Plants and The Movements and Habits of Climbing Plants which perfectly described the enthusiasm, curiosity and accurate observations of the man who, two centuries earlier, laid the foundations of our modern vision of evolution. Following the readings, the voice of a ‘modern’ botanist expounding Darwin’s words took visitors by the hand for a trip back in time, during which time they were invited to look at the most important steps in plants evolution.

In order to help people visualise these steps, a spiral-shaped path was designed on the laboratory room floor by means of a long tissue cloth. Along the path a few potted specimens were placed to illustrate the plant features of sensitivity and movement which mark the most important groups, including Mimosa pudica and Dionea muscipula: both have leaves that demonstrate rapid plant movement (nyctinastic movement) and are representative of the angiosperm group.

On a table a petri-dish was prepared with wild oats seeds (Avena sativa) to illustrate their twisting movement due to the variation in atmospheric humidity and garden cress seed (Lepidium sativum) was grown in glass tubes with agar jelly to illustrate phototropism (growth and response to a light stimuli) and geotropism (turning or growth movement in response to gravity). During the week prior to the ‘party’, one of the glass tubes had been turned upside down once a day so that the stem and radicle clearly showed rotations.

During the evening, a selection of short movie clips were shown from the celebrated TV series The Private Life of Plants by David Attenborough, to illustrate some of the most surprising examples of plant reactions: dispersal, nyctinastic movements, climbing, pollination, etc. The metaphorical step back in time also encouraged visitors to look at the group of gymnosperms and progymnosperms, with their cones perfectly adapted to wind-mediated pollen transport. Graphs were used to illustrate how the perfect geometry of female cones enhances the probability of pollen entrapment and seed dispersal while dormant Gingko seeds were on display to highlight motile gamete fertilisation- a type of fertilisation only occurring in gingkos, cycads, ferns, mosses and algae.

With the help of stereomicroscopes (a microscope used to analyze specimens side-by-side) and magnifying lenses, visitors were able to closely observe a sample of specimens. For example, fern sporangia with spores that can survive for extended periods of time in unfavorable conditions and mosses with their small moving leaves which orient themselves in order to convey and accumulate water drops (their gametes need water, as they move by means of flagella!). Mosses also move to release their spores: they open their spore case lid and enlarge their peristomal teeth to let the spores out.

The final stage of this virtual travel looked at the most primitive members of the plant family, algae. In particular, the focus was on cyanobacteria (also known as blue-green algae or Cyanophyta), which were probably among the first photosynthetic organisms on earth. Scientists suggest that they have a key-role to play in oxygen enrichment of our atmosphere, allowing the ozone layer to form and protecting us from excessive solar radiation. Cyanobacteria also represent the base level of the planet’s trophic pyramid and in the Precambrian era were the primary producers. A digital microscope camera with an image projector allowed people to see examples of the first ever plant movements, those of Oscillatoria ssp.

A beautiful citation from Charles Darwin’s Beagle Diary helped us to feel the emotions he probably perceived when, on the 18th April 1832 he was walking through a forest in Socêgo, Rio de Janeiro:

If the eye was turned from the world of foliage above, to the ground beneath, it was attracted by the extreme elegance of the leaves of the ferns and mimosae. The latter, in some parts, covered the surface with a brushwood only a few inches high. In walking across these thick beds, a broad track was marked by the change of shade, produced by the drooping of their sensitive petioles. It is easy to specify the individual objects of admiration in these grand scenes; but it is not possible to give an adequate idea of the higher feelings of wonder, astonishment, and devotion, which fill and elevate the mind”.

Darwin’s 199th birthday celebration ended with a cocktail accompanied by a special time-traveller dish, Vanilla Pudding which contains vanilla from an orchid (Vanilla planifolia) at the height of evolution and Agar Agar from a seaweed (Gelidium amansii) a jelly thickener from the most ancient plant form, algae!

References

  • Darwin, C. R.., 1880, The Power of Movements in Plants. http://darwin-online.org.uk
  • Darwin, C. R., 1882, The Movements and Habits of Climbing plants. http://darwin-online.org.uk
  • Darwin, C. R., 1882, The Movements and Habits of Climbing Plants. http://darwin-online.org.uk
  • Darwin, C. R., 1839, Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle between the years 1826 and 1836, describing their examination of the southern shores of South America, and the Beagle's circumnavigation of the globe. Journal and remarks. 1832-1836. London: Henry Colburn.

Résumé

En Italie, les visiteurs sont invités à remonter dans le temps à travers l’évolution des plantes au Jardin botanique de Bergame. Dans le cadre des célébrations du 150ème anniversaire de la naissance de Darwin, le jardin a réalisé une exposition ciblée sur les stratégies adaptatives liées aux mouvements des plantes. Ces stratégies, comme le tropisme vers la lumière ou le toucher, ont été extrêmement importantes dans le développement et dans l’évolution des plantes, et Darwin, à la fin de sa vie, fit une étude très vaste sur ces deux sujets. Ce travail a été révolutionnaire pour la botanique ainsi que pour la consolidation de sa théorie de l’évolution. Cette exposition utilise des plantes inférieures, telles que les algues, jusqu’aux plantes supérieures, comme les arbres, pour souligner l’importance du tropisme dans l’évolution des plantes. Des activités pratiques sont proposées et sont une occasion pour les visiteurs d’échanger avec les botanistes et de prendre un rafraîchissement dans la salle de l’ancien laboratoire Sala Viscontea du jardin.

Resumen

Visitantes en el Jardín botánico en Bergamo Italia, han sido invitados a realizar un paseo desde el pasado a traves de la evolución de plantas. Como partea del 150º aniversario de Darwin, los jardines han creado una exhibición enfocada en las estrategias adaptivas del movimiento de las plantas. Estrategias tales como los tropismos a la luz o al tacto han sido extremedamente importantes en el desarrollo evolutivo de plantas y Darwin en sus años posteriores hizo trabajo extensivo sobre ambas. Este trabajo fue revolucionario en la botánica como tambien ayudo a solidificar su teoria de la evolución. La exhibición ha usado desde plantas inferiores como algas hasta plantas superiors como los árboles para resaltar la importancia de tropismos para la evolución de las plantas. Actividades prácticas son ofrecidas y hay una oportunidad para los visitantes de interactuar con botánicos y tomar una bebida refrescante en el jardin de los cuartos de laboratoriao de la Sala Viscontea.

Mara Sugni
Biologist
Orto Botanico di Bergamo "Lorenzo Rota"
Passaggio Torre di Adalberto
2 Bergamo
Italy, I – 24129

Email: mara.sugni@unimi.it