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I find English Ivy to be a fascinating plant for many reasons. One being the changes that it makes from the juvenile stage to the adult stage. Another reason, and the topic of this post, is the way that ivy climbs structures such as trees and walls by the aid of little rootlets.

This is something that has long been observed and was described by Charles Darwin in his book The Movements and Habits of Climbing Plants where he noted two things about the secretions of the rootlets.
Firstly that:

He later described the colour of the cement:


It would seem that after these discoveries, the secretions that provide such successful adhesive properties, were not investigated again until 2007 by Mingjun Zhang and his team at the University of Tennessee in the US.

The aerial rootlets are grown only by the ivy during its' juvenile stage. They can be seen as discs that consist of between four to seven tendrils. To study the tendrils and the secreted materials they encouraged the ivy to climb onto silicon wafer and piece of mica for a week. They then removed these branches so that they could see the traces left on the silicon and mica surfaces. They used Atomic Force Microscopy to get a very close view of the secretion.

They found that the particles were around 70 nm in diameter and very uniform. Each image they took showed a large number of nanoparticles. This provided support for the hypothesis that the nanoparticles play an important role for ivy climbing on surfaces. Also that they are directly related to the capability for the ivy to affix itself.

Not only did they find the immensely small size of the nanoparticle globules that are secrected, but they found 19 different compounds within the secretion. The compounds contain oxygen, nitrogen, and sulphur. Compounds that are well known for their ability to create hydrogen bonds. This suggests that the nanoparticles rely on hydrogen bonding to attach to different surfaces. While hydrogen bonds are known to be weak bonds, over many rootlets, this provides enough force for the ivy to climb surfaces.

The secreted material was shown to by yellow, as documented by Darwin. It is gradually secreted as a gel, with the research team observing that water is evaporated as the gel dries. Once the drying is complete, the stem is firmly attached to the surface. Due to the method of surface climbing, that is, using the rootlets for attachments - the secreted nanoparticles can adhere to various surfaces due to their very small size.

Therefore it seems that it is the many rootlets secreting this weak adhesion along with the hydrogen bonds that are the forces enabling the surface climbing of ivy.

Further Research
As this research was completed some time ago, I wanted to look at what research had been done since 2007. I searched Mingjun Zhang and found that he has been part of some very interesting ivy-related projects. These include understanding the adhesion mechanics of ivy nanoparticles, which could potentially inspire the design and fabrication of nano-bio-materials and the UV protective capability of the nanoparticles of juvenile ivy rootlets, which could be an alternative to metal oxide nanoparticles in sunscreen applications.

It just goes to show that English Ivy, considered to be mundane and a pest to some, is actually a plant at the forefront of research. And most importantly, it doesn't live in some tropical barely explored island - it lives here, with us. Let's take the time to look at it more fondly in future, considering the benefits it give to us and for the secrets it will provide in time.

Resources
Zhang M., Liu M., Prest H. & Fischer S. (2008). Nanoparticles secreted from ivy rootlets for surface climbing., Nano letters, PMID: 18355053Darwin, Charles (2011-03-24). The Movements and Habits of Climbing Plants (Kindle Locations 1438-1439 and 1824-1825). Kindle Edition.  

A few years ago English Heritage funded research into the role that English Ivy (Hedera Helix) plays with regard to historic monuments. The idea was to find out, over 3 years, the positive and the negative impact that ivy can have on historical walls and buildings, as well as how to manage the ivy.

I volunteer at a Living Churchyard where there is plenty of ivy. I'm quite a fan of it, but realised that I knew next to nothing about it. So I decided to read the seminar report PDF produced for English Heritage so I could have a better understanding of whether my fan-status of ivy was justified.

The research focussed on:

1. Temperature and humidity conditions at the wall face. Conditions behind a layer of ivy compared to uncovered walls. Anything which moderates the freeze/thaw cycle or the wet/dry cycle may be potentially protective.
2. The mechanism of attachment. How the aerial rootlets stick to walls and if this causes damage. Understanding how these rootlets adhere helps to determine the severity of damage caused.
3. What causes the ivy to send ‘proper’ roots into walls. These roots, unlike aerial roots, are not normally produced by climbing stems and are damaging (displacing masonry, causing cracking, and possible destabilisation).
4. Particulate filtering. Whether ivy leaves prevent dust and pollution particles from reaching the wall surface. If ivy does, then this could potentially reduce deposition of damaging pollutants on to vulnerable wall surfaces.

The results gathered from the experiments in the field and the lab showed the following:

1. Temperature and humidity conditions at the wall face. Hourly data showed a general mediating effect of ivy canopies on both temperature and relative humidity over the five sites used in the project. iButton Hygrochron recording devices were used to monitor temperature and relative humidity.
• The ivy reduced the extremes of temperature and relative humidity – the most clear-cut differences found for temperature. On the five sites used for the project – exposed surfaces were 36% higher and 15% lower than ivy covered surfaces.
• The ivy affected the diurnal range in temperature and humidity throughout the year. The average showed that exposed surfaces had a mean daily temperature range 3.6 times greater AND a humidity range 2.7 times greater than those of ivy covered walls.
• Important factors influencing results: shading by trees or other walls, aspect of the wall and thickness of the ivy canopy.
2. The mechanism of attachment. This is an ongoing part of the project. The report mentions that no damage has been recorded from the rootlets as yet on the test wall – but does not go into detail about the mechanism of attachment. Page 33 of the report notes that careful removal of ivy from limestone revealed ‘fresh and clean surfaces’.
3. What causes the ivy to send ‘proper’ roots into walls. This is another ongoing part of the project. The report mentions that the ivy on their test wall has not produced any roots as yet. Page 35 of the report notes that where ‘proper’ roots were seen by the investigators it was because the ivy was cut off at the base in an attempt to kill it off. Roots were seen only where there were holes in the wall.
4. Particulate filtering. The project examined three sites in Oxford to assess how the ivy interacted with airborne dust and pollutants. A scanning electron microscope was used to investigate the deposition of particulate along the roadways of these three sites. The findings showed that ivy trapped particulate matter and acted as a ‘particle sink’ – especially in areas with high volumes of traffic. The results show higher amounts of particles (per mm2) on the outer ivy canopy than on the inner parts of the canopy. The separate paper detailing the results of particle filtering suggests that ivy and other higher plants could have potential in conservation as a protective layer that mitigates particulate deposition on historic stone surfaces in metropolitan areas.

The research team took a broad view of the major processes of deterioration that affect masonry walls:
Physical: Freeze-Thaw, Wetting and Drying, Heating and Cooling, Salt weathering.
Chemical: Runoff- or rising damp-induced chemical weathering, Pollution-induced chemical weathering.
Biological: Roots, Lichen weathering, Microbial weathering.

Which helped them interpret the results from the study and discuss the roles that ivy plays:
Positive roles of ivy

• Passive roles of ivy: may prevent excessive heating and cooling- moderating freeze/thaw; may regulate humidity and stop rainfall hitting the wall – reducing chemical weathering; may absorb pollutants and salts – reducing weathering

Negative roles of ivy

• Passive roles of ivy: may keep walls damp through reducing evaporation – potentially enhancing chemical weathering

• Active roles of ivy: roots penetrate vulnerable walls and cause physical breakdown; aerial rootlets may chemically deteriorate vulnerable minerals.

Ivy Removal
Importantly, the study also looked at three methods of ivy removal. Firstly, cutting the ivy at the base to let it die before removal. Secondly, poisoning the ivy in an attempt to kill it before removal. Thirdly, removing the ivy carefully with no other treatments. They found that:

• Cutting the ivy off at the base and leaving it to die is detrimental to the wall as the plant may grow sporadically – potentially causing damage to the wall.

• Poisoning the ivy can pull of mortar and additional work may still be required to fully remove the plant from the wall. Poison may also damage other plants close to the ivy plant.

• Gently removing the ivy with no other treatments to be the best method.

I find it exciting that this type of research is receiving funding as it can provide new knowledge for the wider community as ivy is so common and isn't selective towards historic stone buildings to climb up. This research can help us consider the state of the structure ivy is growing up and if ivy will benefit the wall (if it's in good condition), or perhaps where ivy needs monitoring or managing, especially if the wall is in poor condition.

As this post is getting a bit long, I'll write about my thoughts on ivy in a future post! Until then, it'd be great to hear your thoughts about ivy in the comments :)

Resources
Sternberg T., Viles H., Cathersides A. & Edwards M. (2010). Dust particulate absorption by ivy (Hedera helix L) on historic walls in urban environments, Science of The Total Environment, 409 (1) 162-168. DOI: 10.1016/j.scitotenv.2010.09.022
http://www.geog.ox.ac.uk/research/landscape/rubble/ivy/

Ever since watching the television programme Wild Things and hearing about the genetic mutation that occurs every seven years and results in a plant with additional petals, I've been on the look out for such a plant. Which along with research about the buttercup lights up your chin, will be discussed in part 2 of this study. Part one is available here.

Imagine my surprise when one popped up in my back garden! Normally creeping buttercup has 5 petals, but there are plants that flower with additional petals. The additional petals can also be used to date meadows in which they occur.

As creeping buttercup primarily reproduces by sending out creeping runners, a meadow of hundreds of buttercup flowers can be made or just a few plants. This means that each new plant created by this vegetative reproduction carries identical genes to the parent plant. Over time some of these genes begin to mutate (somatic mutation), resulting in flowers with an extra petal.

A 2011 study found that each plant that flowers with additional petals in a sample of 100 plants was found to equate to approximately 7 years. Therefore a meadow with a known age of around 100 years could be expected to contain about 14 flowers with these extra petals. This method works well in estimating meadows up to 200 years old.

But this isn't the end of the wonders of the buttercup, as research published in 2011 goes to show. A research team look in to the 'directional scatter' from the buttercup flower. This directional scatter is often used by children holding a buttercup under a friend's chin to see if they like butter.

Directional scatter, as displayed by my beautiful assistant.

The earliest documented research regarding this was done by Mobius in 1885, who showed that the oily appearance of the yellow flower is caused by a pigment. This current research found that the structure of the petal, particularly the epidermal layer has a large part to play. The epidermal layer is the outermost layer, and is akin to our skin. In the buttercup petal the epidermis has two extremely flat, semi-transparent surfaces that bear pigments that reflect yellow light with a high intensity. The epidermis is separated from a paper-white starch layer in the petal by a layer of air. This interplay between the layers serves to double the gloss of the petal allow for a highly directional reflection.


So the next time you're in a field playing the game to find out who likes butter, remember is has nothing to do with whether you like butter. Instead it is all to do with the biology of the buttercup and the lengths it will go to attract potential pollinators! Oh, and while you're there you may as well check for some 6 petalled buttercup flowers - perhaps they might become the new 4 leaf clover.

References
Warren J. (2009). Extra petals in the buttercup (Ranunculus repens) provide a quick method to estimate the age of meadows., Annals of botany, PMID: 19491088 
Vignolini S., Thomas M.M., Kolle M., Wenzel T., Rowland A., Rudall P.J., Baumberg J.J., Glover B.J. & Steiner U. (2011). Directional scattering from the glossy flower of Ranunculus: how the buttercup lights up your chin., Journal of the Royal Society, Interface / the Royal Society, PMID: 22171065
Carotinoids and Related Pigments

Ivy flowers. Copyright: Alfred Osterloh

With great pride I support our English Ivy (Hedera Helix). I think that in the right situation it's a feast for the eyes and a wonderful resource for all of nature - us included. Ever since I was a lad I'd heard all the negative press about ivy being parasitic (which it's not) and that it damages everything it climbs upon (which it does not), so earlier this year I did my own research and documented the most current findings on the positives and negatives of ivy and how to manage ivy on my blog here. I also wrote about research into the weak, but potentially important, adhesion that ivy rootlets secrete here.

With that in mind, I was very excited to read research published earlier this year evaluating the importance of ivy (Hedera helix and H. hibernica) for autumn flower-visiting insects, particularly honey bees. Not only were the findings positive, but the researchers went as far as to say that:

Keystone species are species that play a crucial role within the ecosystem(s) that they are present. Keystone species can affect many other organisms within the ecosystem to the point of determining the numbers and types of other species within the ecosystem community.


To see why the researchers have made this suggestion, we need to consider which species visit the ivy flowers, what the ivy flower offers, and what benefit these species derive from a relationship with ivy:

• Firstly, there were many different species visiting the flowers of the ivy including the honey bee (Apis mellifera), common wasp (Vespula vulgaris), ivy bee (Colletes hederae), hover fly (Eristalis tenax), green bottle fly (Lucilia sp.) and red admiral butterfly (Venessa atalanta) among others.

• Secondly, the ivy flower offers both nectar and pollen, possibly no surprise there. But, perhaps what is surprising is that the nectar has a sugar content of around 49%. This is quite a high percentage and shows that ivy nectar is a high quality foraging resource. The results strongly suggested that the only nectar that the tested bees had in their crops was from ivy. This becomes even more important considering that 79.7% of honey bees and 94.6% of bumble bees did not have pollen in their baskets. Pollen trapping at six hives in two locations showed that of the pollen that was collected by the honey bees, an average of 89% was pollen from ivy during the autumn.

• Thirdly, ivy is a very abundant plant meaning that foraging distances are much shorter than summer foraging trips. Collecting pollen and nectar from ivy flowers is also fairly easy. These traits make it efficient enough for honey bees to make a honey crop. This may improve survival over winter of honey bees. These factors may well provide honey bees with a food resource allowing them to rear young workers before overwintering, subsequently providing them to get off to a great start in the spring. The paper rightly suggests that further experimental work should be done before we can understand this properly.

So, while we already knew that ivy provides food via berries and can provide a home for many insects and nesting sites for birds (if it is allowed to grow), but this paper really drives home the importance of ivy to many species of insect that are still around in autumn, including late season butterflies.

Ivy not only provides them with a meal as they collect nectar or pollen, but the nectar is of such high quality it can also help honey bees survive the winter. Without sounding too dramatic, if ivy was lost to the ecosystem, even locally, it could mean death to the honey bees in that particular area. If honey bees aren't around to pollinate our food crops, then we could be in big trouble.

It just goes to show how difficult it can be to understand ecosystems and food webs, prior to this research I wouldn't have connected ivy to food crops and yet the honey bee is a link between the two.

For further information on this paper

• Watch a video made by the University of Sussex produced to assist us in identifying the insects we may see on ivy flower:

• To read more, view some amazing macro shot, or download an ID leaflet; see the University of Sussex blog post about the research here.
• Read the AOB blog post that alerted me to this research.
• Also, interestingly, a house that had been allowed to be overrun by ivy for 10 years recently had the ivy trimmed back. While some of the dead ivy branches were left hanging for some reason, this house shows that as long as the masonry and brickwork aren't damaged prior to the ivy - then they won't be damaged by the ivy. To see the photos, click here. 

Reference
Garbuzov M., Ratnieks F.L.W., Leather S.R. & Roubik D. (2013). Ivy: an underappreciated key resource to flower-visiting insects in autumn, Insect Conservation and Diversity, n/a-n/a. DOI: 10.1111/icad.12033

Many plants have a tendency to lean towards the light. Until Charles Darwin and his son performed what is now a famous experiment in botany, sparking detailed investigations into how plants grow towards the light, spanning three centuries.

1880 - The Darwin Experiments
Most famous for his seminal book, On the Origin of Species, Charles Darwin's work on botany was just as important. Darwin and his son Francis wrote a whole book observations regarding how plants respond to stimuli, The Power of Movements in Plants. They thought that plants could grow differentially and therefore in the direction of the light

The Darwin experiments, used oat coleoptiles. The experiment modified the growing conditions of these coleoptiles so that the response could be observed:

Some of the many experimental modifications to test for a reaction to light stimulus.

A - The coleoptile with no modifications: A bend towards the light can be seen.
B - The coleoptile with tip cut off: No response to light.
C - The coleoptile with tip covered with opaque cover: No response to  light.
D - The coleoptile with tip covered with transparent cover: A bend towards the light can be seen.
E - The coleoptile with base covered with opaque cover. A bend towards the light can be seen.

They demonstrated the following:

1. Not only did they find that the oat coleoptiles do bend towards a light stimulus, but that it was the tip of the plant which is active in initiating this response. 
2. This also showed that while it was the tip that perceived the directional light, the reaction happened further down the stem. 

This led Darwin to posit that there was an 'influence' that moved from the site of perception to the site of reaction. 

However, it wasn't until the following century that scientists were able to find out what this influence was.

1920s and 1930s - The Cholodny-Went Model
The experiments of Nicolai Cholodny, who worked with grass roots, and Fritz Went who worked with grass coleoptiles, progressed the knowledge provided by the Darwin experiments. Just as Darwin and Wallace discovered Natural Selection independently, Cholodny and Went independently made the same hypothesis which gave a name to Darwin's 'influence'.

They found that an asymmetric accumulation of auxin occurs in the stem as a response to the unidirectional light.

This means that there is differential growth in the plant stem. This happens when the transport of the plant growth regulator auxin accumulates on the side of the stem furthest from the light source - making those cells grow more rapidly. The auxin is transported from the side of the stem that is closest to, or receiving, the light - whose cells grow more slowly.  With one side of the stem growing faster than the other, a bend is created that is directed towards the light source.

2013 -  Research by Technische Universitaet Muenchen (TUM) and Université de Lausanne (UNIL)
The Cholodny-Went model, while popular was not the only hypothesis. It was also noted that plants with known defects in auxin transport still responded perfectly well to unidirectional light stimulus. This story has only this year seemed to reach a conclusion to this important, yet seemingly simple, question.

New research has confirmed that the Cholodny-Went model is correct. Scientists from UNIL inactivated several PIN transporters, important for proper cellular coordination, while scientists from TUM demonstrated the function of the D6 protein kinase, important for the regulation of PIN-mediated auxin transport.

They found that without these transporters and kinase components the plant was unresponsive to light signals that would have previously triggered phototropism.

Therefore we now know that Darwin's 'influence' - the auxin discovered by Cholodny and Went - is definitely the substance that the plant uses to mobilise the bending towards the light in response to blue light.

To read more about this new research, click to visit Science Daily or the original press release from TUM.

References
Willige B.C., Ahlers S., Zourelidou M., Barbosa I.C.R., Demarsy E., Trevisan M., Davis P.A., Roelfsema M.R.G., Hangarter R. & Fankhauser C. & (2013). D6PK AGCVIII kinases are required for auxin transport and phototropic hypocotyl bending in Arabidopsis., The Plant cell, PMID: 23709629