Dr. William Lauder Lindsay, a physician and a botanist wrote in 1876: “It appears to me that certain attributes of mind, as it occurs in Man, are common to plants.” Other scientists have since come to the conclusion that while we are the most intelligent among all animals, humans are not the only ones that display this biological property. The precursor to plants and animals had already genetics that during evolution were shared by both plants and animals. The implications of the studies described below in this post, and many others, show that evolution was based on the inheritance of acquired characteristics, as claimed by Jean-Baptiste Lamarck. Biological intelligence is a part of our genetic make-up, like the shape of our body, and is present in similar, but not in the same form, in all creatures. In his ‘Power of Movement in Plants’, Darwin wrote: “It is hardly an exaggeration to say that the tip of the radicle (root) thus endowed , and having the power of directing the movement of the adjoining parts, acts like the brain in one of the lower animals.”
Today scientists from various universities, working on developing Darwin’s root-brain hypothesis, use the term ‘plant neurobiology’ that points to the similarities between plants and animals. Of course, we must remember that evolution created specific sets of cells, tissues and organs. While animals developed weight-supporting skeletons, plants have developed woody trunks. The issue of the degree of plant intelligence is not as yet fully understood, and needs more studies. What we know now is that plants are able to differentiate between red, blue, far-red and UV lights and respond to them. They know that they are being touched, can respond to compounds in the air and they can hear. They know gravity and respond by growing up, but putting roots down. They are aware of their past and accordingly modify their present physiology as they remember their previous experiences, like infections.
As yet, we don’t have the knowledge to prove if plants can suffer or be happy in our understanding of the term, but it also means that we cannot disapprove of the terms being used. Most good gardeners think that well-looked after plants do look happy, and wilting ones do not, but it is still an unanswerable question. Darwin’s experiments to establish whether the tip of the plant senses gravity, then passes this information along, instructing the plant to grow the roots down, and the top towards the light and up, was successful in positively answering this particular question. But even this issue is much more complex when looked at today. Advanced studies using advanced microscopes revealed the complex subcellular structure of roots. Part of the root cell contains a heavier than the rest of the cell structure that researchers call statoliths, from the Greek, meaning ‘stationary stone’. Further research, including taking plants under weightless conditions (effectively zero gravity) in spacecraft, has confirmed that the presence of statoliths is necessary to react to gravity and grow roots down. In spacecraft, roots were growing in every direction.
It is extraordinary and inspiring to think what is going to be discovered in the next century. When Darwin designed his experiment to find which part of the plant can see the light, and found it was the tip, which then passes the information to the stalk and which then bends towards the light, he didn’t know that years later a Danish plant physiologist Peter Boysen-Jensen would use this knowledge to expand the findings. Like Darwin, he cut the tip of two plants and then used a piece of glass between one tip and its stump, and a thin slab of gelatin between another tip and its stump. The plant that had the gelatin reacted to the light by bending, while the one with glass did not. It was obvious that the bending signal coming from the tip must be soluble since it could pass through the gelatin but not through glass. Later on, in the 1930s, it was discovered that it was a growth-promoting chemical called auxin (Greek for ‘increase’). It is a very prevalent hormone as it has a major function of making a plant to bend towards the light, and grow better and faster.
Do plants have memory? In an experiment in 1977, a scientist, Mark Jaffe, wanted to prove that plants have procedural memory, that is they are capable of sensing and reacting to external stimulation. He cut a tendril of a pea plant, known to coil around anything that would support it, and kept it in a well-lit environment. To get it to coil he rubbed the tendril with his finger. When he put the tendril in a dark place, it would not curl as it needed light to perform. But when he placed the pea tendril in the light, two hours later, it would spontaneously curl without the stimulation of the scientist’s finger. The tendril stored the information of being touched and coiled as soon as it was put in the light. This is a type of procedural memory.
The research into genetics in the Soviet Union was led by the scientist, Lysenko, who was one of the first to establish that some plants need very cold weather to flower. When the winter was mild and various crops would fail, he found a solution. The seeds were put into a freezer, and then planted in the spring, and not as it had been done previously in autumn, and the plants flowered, ensuring good crops. It was clear that the seeds remembered that they had the cold period they needed and flowered as it was April, the time they usually have done so in the spring. Lysenko proved that this most important process could be artificially manipulated, and he was venerated for saving masses from starvation. Later, scientists discovered that the cold treatment triggers a change in plant DNA structure, which is then passed on to the next generation of female cells. It is truly astonishing that plants not only have the memory from season to season, but can also pass it from generation to generation. Recent studies in Switzerland established that plants under stress make a new combination of DNA, that is also passed to a new generation.
The press reported recently that pollinating experts, honeybees, are also adept in maths. The bees were taught to recognise the colours as plus or minus symbols. After achieving this, scientists then taught honeybees to solve basic mathematical problems. It involved addition and subtraction, and the success rate was 75%. Prof.Adrian Dyer from RMIT University in Melbourne wrote: “Our findings suggest that advanced numerical cognition may be found much more widely in nature among non-human animals than previously suspected. If maths doesn’t require a massive brain, there might also be new ways for us to incorporate interaction of both long-term rules and working memory into designs to improve rapid learning of new problems.”
The discovery that bees can understand the concept of zero, lead to further research. Fourteen bees were trained to enter a Y-shaped maze consisting of a tunnel with two opposite exits. When they got into a tunnel the bees saw different shapes coloured either yellow or blue as ‘numbers’ arranged in sums. The bees were trained to follow correct sums to their reward of sugary water. Those that followed a path marked by an incorrect sum only got a bitter solution. After 100 trials the bees learned to get the right solution. The scientists pointed out that to be able to solve even basic maths problems requires the ability to understand abstract rules. Prof. Dyer said “You need to be able to hold the rules around adding and subtracting in your long-term memory, while mentally manipulating a set of given numbers in your short-term memory”.
These are true wonders of the natural world; how many more astounding discoveries are we going to find in the future?