MissGreenDreamz
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What is ‘sentience’? When a person or animal is injured they react by experiencing pain, marshalling the body’s defense systems to repair the damage and begin the process of recovery. The question, surely, is whether we know enough about sentience to be quite certain that plant life does not have it.
Every ecologist out there, and even amateur gardeners, have been known to swear that plants, too, ‘feel’ things, but it is only recent research that has demonstrated just how ‘intelligent’ they really are. Plant life has a heritage far older than mankind, and in some respects, it makes we humans seem inadequate! Is it not about time to take more notice?
It is now known that plants have, admittedly in different forms, the same innate abilities as those with which animals and humans make sense of their environment. They see, smell, taste, feel and even listen to their surroundings. Even as seeds, ready to germinate, it’s been proven that they are sensitive to as many as twenty different factors – like the season of the year and where the light is coming from – information they need to decide the right time to start growing!
A truly remarkable ability to ‘smell’ their surroundings is vital for all plants. Even seeds can detect chemical components of smoke which prompt them to germinate – a natural way of replacing flora lost to forest fires, for example. Trees have defence mechanisms built around this ability. When one tree is attacked by pests, it emits chemical signals to nieghbouring trees, encouraging them to produce chemical deterrents to that pest, ensuring their own safety.
Dutch scientist Marcel Dicke, of the Agricultural University in Wageningen, Holland, found evidence that all plants perform similar actions to the trees, when under threat from predators. Indeed, the level of sophistication in this process is made all the more remarkable by the fact that the these ‘signals’ encourage production of substances tailored to specific pests!
An example of this would be the lima bean. When attacked by spider mites, the plant releases a chemical attractant for other types of mite, which prey on the attackers. Some plants help others, as in the case of cabbages, which release foul smelling isothiocyanates, discouraging aphids from attacking neighbouring plants like broad beans.
Research has also shown that plants actually ‘time’ the release of defensive chemicals, to correspond with the hours of the day when predators are most active. US Department of Agriculture studies in Gainesville, Florida, showed that maize and cotton plants, damaged by certain pests, increased output of chemical ‘help’ signals to pest-killing wasps at the time of day when the wasps are most active.
Do plants really know when something touches them? If you stroke the leaves of a mimosa plant, they react by closing up at once. Research has shown that in 17 different families of plant, over 1,000 varieties are very sensitive to touch – possibly an ancient inheritance from bacteria, which are known to be the ancestors of all plant life, responding to stimuli with minute electrical impulses.
The best known ‘touch sensitive’ plants are predators, like the Venus Fly-trap, but this sensitivity is, in some respects, common to all types of plant life, albeit in slower, less immediately noticeable ways. American research, by Professor Mordecai Jaffe in North Carolina, has shown that simply touching and stroking a plant stem, for a few seconds each day, will encourage a thickening of the stem.
The plant reacts as if it is being subjected to strong winds, and takes appropriate defensive measures. This reaction is used in Japan to ensure strong canes of sugar beet, by striking young plants with broom handles before transplanting them. Amateur gardeners can benefit, too, by stroking young seedlings before planting them out.
It was in the early years of the last decade that two British scientists, Norman Biddington and Tony Dearman, conducted tests in Warwickshire, proving that stroking young plants with bits of paper actually helped them to combat the effects of both drought and frost, when planted in the outside environment.
Professor Jaffe says, laughing, that one would have to talk to one's plants for weeks before noticing any results, but there is no doubt that plants are very sensitive to sound. They respond best to noises just outside the volume of the human voice, at 70 to 80 decibels. If subjected to regular bursts of sound at this level, some plants can actually double their rate of growth, and some seeds will germinate as much as 80 to 90% faster.
The most amazing thing about plants is their ability to ‘see’. So sensitive to light are they that even the colour of their surroundings can affect their growth and taste! A molecular biologist at Glasgow University, Gareth Jenkins, ran tests proving that proteins within plant cells – called cryptochromes and phytochromes – are extremely light sensitive. So much so, that their ‘sight’ encompasses wavelengths well beyond the range of human vision.
The plants sense also the direction of the light source, and when the Sun comes up, enhance production of the colourless pigments – quercetin and kaempferol – which help screen them from the more harmful effects of sunlight. Remarkably, the work of Michael J Kasperbauer, US plant physiologist – he’s spent thirty years researching light sensitivity in plants – is causing a real stir among the farming communities.
Kasperbauer found that the phytochrome protein is colour sensitive to a degree possibly far beyond that of animals and humans. So much so, that the minute variations in the wavelengths of different colours can make a big difference to plant yields.
In more recent times, many growers plant crops atop great swathes of black plastic sheeting – to retain moisture, discourage weeds and insulate young roots. This has the beneficial effects of reducing the waxiness of plant leaves – thus helping them to retain water more easily, and encouraging the plant to develop resistance to pests.
The professor showed that changing the colour of the sheeting really can improve both quantity and quality of yield, and even affect the flavour! The secret lies in the fact that the phytochromes in the plants are especially sensitive to the red and ‘far red’ wavelengths.
If they detect these, they signal that the plant must grow faster and stronger – competing for space because the light makes them respond as if they are hemmed in by other plants, competing for the nutrients. To improve their own chances of dispersing seed for the next generation, they grow taller, and develop more fruit. The tests showed that yields increased by between 20 and 50% when red sheeting was used instead of black.
Kasperbauer even showed that different coloured sheetings can actually affect the taste of the crop. Turnips were grown on blue, white and green sheeting, and testers reported that the resultant vegetables tasted ‘sharp’, ‘bland’ or ‘almost sweet’ according to the colour. It would seem that the right approach to the planting of crops, in colour terms, could be of enormous benefit to humanity.
It is now believed that plants have an ability to ‘taste’ their surroundings. Research at the Institute of Arable Crops, in Hertfordshire, England, has revealed a particular gene in plants, which enables root systems to taste the surrounding soil – moving in the direction of the richest sources of nutrition and ammonia, which they need for ‘fixing’ nitrogen. This taste ability is also used in self defence. When a plant ‘tastes’ the secretions of a parasite, it immediately begins to produce defensive substances.
Prince Charles, heir to the English throne, has long been an outspoken supporter of organic farming methods, and indeed studies have shown – particularly in third world countries – that far less use of pesticides leads not only to healthier and more nutritious crops, but in many cases to a large improvement in the crop yields that such farming produces. It now seems abundantly clear that, in centuries past, when farmers had no choice but the organic route, sustainable growing areas were much easier to retain over long periods
There is no doubt that plants are far more adaptable than people might ever have believed, nor that they are well equipped to deal with the difficulties that nature might place before them. They have superb defensive mechanisms, respond positively to the right stimuli, and will, if treated properly, yield food and pleasure in great quantities. If sentience were to be measured by the ability to react to the outside world, then surely they would have to qualify?
As professor Anthony Trewavas, of Edinburgh University, put it: ‘Plants are not as stupid as people think……in fact, in some ways their intelligence exceeds that of humans.’ Perhaps, one day, we will be able to fully comprehend the ways in which plants communicate, and even open up dialogue with them. In the meantime, it would be in our own best interests to remember that plants, like ourselves, really do have ‘feelings’, and that we should give them the respect they truly deserve.
© Leather 2005
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