The Sensitive Plant

"A Sensitive Plant in a garden grew,
And the young winds fed it with silver dew,
And it opened its fan-like leaves to the light.
And closed them beneath the kisses of Night."

This poem by Percy Bysshe Shelley meanders on for 311 lines, and I recommend taking the time to read it not only for its lyric beauty, but also for its description of the senses of a garden.

What is the "sensitive plant" of which Shelley writes?

The most famous sensitive plant is Mimosa pudica which is native to South and Central America, but is now grown worldwide as an ornamental plant because of its fascinating moving leaves. The Mimosa’s leaves are hyper-sensitive to touch, and if you run your finger down one of its leaves, all the leaflets rapidly fold inward and droop. They reopen several minutes later, only to rapidly close once more if you touch them again. The name “pudica” reflects this drooping movement. It means “shy” in Latin. The plant is also known throughout many regions as “the sensitive plant”. Its unusual behavior is referred to as “false death” in the West Indies, it is referred to as the “don’t touch me” plant in Hebrew, and in Bengali it is called the “shy virgin”.

The drooping and opening action that is characteristic of the Mimosa is regulated by electricity. This was noticed by Sir Jagadish Chandra Bose, a noted physicist turned plant physiologist from Calcutta, India, back at the beginning of the 20th century. Bose reported to the Royal Society in 1901 that touch initiated an electric action potential which radiated the length of the leaf resulting in the rapid closing of the Mimosa leaflets.

The Dragon's Blood Tree

Sometimes nature provides such beautiful surprises in the forms and shapes it builds.

Dracaena cinnabari, or as it is commonly referred to, the dragon's blood tree, is found only on the Socotra islands, off the Horn of Africa and to the south of Yemen. As often happens in isolated ecosystems (think of the Galapagos) wondrous and diverse species developed on this archipelago.

These trees which resemble gargantuan mushrooms are actually a unique type of monocot, similar to palm trees. But different from all other monocotyledonous trees, the dragon's blood tree continuously branches, with leaves only forming at the ends of the young branches. This gives it its distinctive shape. 

The name "dragon's blood" derives from its dark red resin which has numerous practical and medicinal uses for the natives.  

What A Plant Hears?

An example form The Telegraph of research into plant hearing

While loads of research support the idea that plants see, smell, taste and feel, support for plant auditory prowess is indirectly proportional to the amount of anecdotal information we have about the ways in which music may influence how a plant grows. Many of us have heard stories about plants flourishing in rooms with classical music. Typically, though, much of the research on music and plants was carried out by investigators who were not necessarily adhering to the controls found in laboratories grounded in the scientific method. Not surprisingly, in most of these studies, the plants thrived in music that the experimenter also preferred. 

In retrospect perhaps, these musical experiments were doomed from the start. What relevance would human music, whether baroque or bebop, be to a plant? When studying plant vision we don’t show a plant an eye chart and ask it to read the bottom line, and in studying plant olfaction, we don’t ask it to differentiate between Chanel #5 and Old Spice. Rather we study the sense in an ecological and evolutionary relevant setting.

A very recent paper from the laboratory of Stefano Mancuso in Italy attempts to apply rigorous standards to determine what exactly plants hear and how this affects plant development. Their preliminary results show that not only do corn roots apparently grow towards specific frequencies of vibrations, but roots themselves may also be emitting sound waves! Hopefully, studies like these will move us away from the ridiculous question of what music plants prefer.

If this line of research pans out, I'll have to rewrite Chapter 4 of WHAT A PLANT KNOWS (which by the way goes on sale today)!

Plant olfaction - Plants smell?

Common dodder (Cuscuta pentagona)

Cuscuta pentagona is not your normal plant. It is a spindly orange vine that it basically has no leaves. What's unique about Cuscuta is that it isn’t green, because it lacks chlorophyll, the pigment that absorbs solar energy, allowing plants to turn light into sugars and oxygen through photosynthesis. Cuscuta gets its food from its neighbors; it is a parasitic plant. In order to live, Cuscuta attaches itself to a host plant and sucks off the nutrients provided by the host by burrowing an appendage into the plant’s vascular system. What makesCuscuta truly fascinating is that it has culinary preferences: it chooses which neighbors to attack.

The way Cuscuta does this is through its sense of smell. Yes Cuscuta, like all plants, can sense volatile chemicals in the air, just like we can sense, can smell, bleach that's been used to wash a floor, a neighbor's barbecue a few houses down the street, or a new perfume squirted into the air. Cuscuta uses the smell of neighboring plants to find the tastiest one to attach on to. Cuscuta tells the difference between plants by the way they smell; Cuscuta can differentiate between tomato and wheat, and given the choice will prefer a tomato plant!

You can read more about Cuscuta and a plant's sense of smell here, or in Chapter 2 of WHAT A PLANT KNOWS.

Pretty but poisonous

Sophora secundaflora (Texas mountain laurel)

The Texas Mountain Laurel is a lovely small tree with bunches of bright blue flowers. These flowers yield bright red seeds which Native Americans used as ornaments and jewelry, but also as an hallucinogen. The seeds can be used to make a drink which when dilute leads to hallucinations, but at higher doses is poisonous. The toxic compound, cytisine, causes paralyses which leads to suffocation.

Very, very old plants

~1500 year-old Welwitschia mirabilis 

The Welwitschia plant from the Namibia dessert can live for up to 2000 years. What's really strange is that the leaves of Welwitschis are the parts that keep growing continuously. While the tips of the leaves eventually fray and die, the base keeps growing, pushing out new parts of the same leaf sort of like a vegetal pasta machine!

Yesterday-today-and-tomorrow

Brunfelsia pauciflora (yesterday-today-and-tomorrow)

The Brunfelcia is a small shrub with beautiful pansy-like flowers. Yesterday-today-and-tomorrow is aptly named as its flowers begin life with a deep purple color which change to lavender, and finally fade away to white. While native to Brazil, this evergreen shrub has been cultivated and is used in gardens indoors and out. It also contains a neuro-active drug called "scopoletin". Animals or people who mistakenly eat this plant develop an irregular heart rate, dryness of the mouth, dilated pupils, and in rare cases, coma. In controlled dosage, this chemical can be used as a medicine.

Guest Blog: Dr. Yuval Sapir and the Lily from the mountains

Lilium candidum - Madonna lily

Dr. Yuval Sapir is Director of the Tel Aviv University Botanical Gardens 


The crusaders fell in love with the large white, trumpet-like flower of Lilium candidum when they arrived in the middle east. These christian believers immediately took the lily as the sign of the Annunciation, when according to Christian lore, the Angel Gabriel told Mary that she would give birth to the son of God.

What could cause these European religeous warriors to consider the lily the flower of the Annunciation?

Well, lilies flower religiously (all pun intended) towards the end of March. Count nine months forward from the end of March, and you get December 25. So of course the flowering of this marvelous flower must have religious meaning. Thus they termed this majestic, pure white flower the Madonna Lily.

The Crusaders picked and shipped thousands of Madonna Lilies back to Europe, where its cultivation failed miserably. Over the years, another species of Lily - Lilium longiflorom - was adopted as a proxy for the Madonna Lily. This species is from Eastern Asia, and defined (as the name hints) by longer flowers than the Middle-Eastern lily.

The Madonna Lily still grows naturally in Israel in the upper Galilee and on cliffs in the high Mount Carmel. It is among the rare and endangered plants in Israel, but also among the most pilgrimaged ones, because of her beauty. It became the symbol of the Tel Aviv University Botanical Garden, based on a picture that Prof. Jacob Galil, the founder of the garden, took in the 1950's.

Priorities for Plant Scientists

We biologists like to think that the scientific agenda followed in our labs is predominantly rational. But the subjects we study are as often determined by serendipity as by rational planning.

How refreshing then that a group of European, primarily British scientists, recently conducted a study to identify the 100 most important questions facing research in plant sciences.

A hundred questions is rather daunting, and of course many are intimately connected with each other. But I’d like to focus on two of these questions, and tell you why they not only are they the most important questions for plant scientists, but actually the most important questions for all scientists.

#1 (and it should come as no surprise): “How do we feed our children’s children?”

Wheat field in Hod Hasharon, Israel

Most models have the world’s population reaching 9 billion by 2050. That is a 3-fold increase in my lifetime alone. If we consider that these 9 billion will live on a planet with less arable land, less fresh water available for agriculture, and with dwindling supplies of chemicals for fertilizers, the potential for problems in food availability, let alone a full-blown food disaster, is pretty obvious. Throw into this equation that these 9 billion will be more prosperous, demanding more meat and dairy then used today, then the demands on food supplies become precarious.

So at the risk of insulting colleagues and friends, and with all due respect to modern medical research, I think it is clear that if we do not solve the problems of ensuring a future food supply, then questions of cures for cancer and Alzheimer’s disease become moot.

When I made this statement a few years ago at a workshop, a very prominent scientist grabbed the microphone and said, “If we feed the world, there’ll just be more people!” GASP!

Students working in the Manna Center for Plant Biosciences

Assuming we don’t agree with this rather Archie Bunkerian statement, we come to question #2 (which was actually #9 on the list): “How can we attract the best young minds to plant sciences so that they can address Grand Challenges facing humanity such as climate change, food security and fossil fuel replacement?”

Any hope of scientific and technological progress is fully dependent on human resources. The Manhattan Project and the 1960’s space program are clear examples of how harnassing the brightest young minds to a clear goal can lead to breakthrough results. But to be frank, we have not been successful until now in attracting droves of the brightest, most talented students to plant biology.

This is not a knock to the current generation of plant scientists and their students, but a statement of fact that in terms of facilities, grants, scholarships and prestige, plant sciences, at most universities take a back seat to biomedical research. Students, who are often attracted as much, or not more, to prestige than to a particular field, are then understandably drawn to the new prestigious programs and facilities in, for example, neurosciences.

Attracting new talents into plant research will necessitate far-reaching programs and investments. As Deep Throat infamously said, “Follow the money”.

Sainsbury Laboratory

And students and scientists alike do follow the money. The new Sainsbury Laboratory at Cambridge University is prime example of how to attract young minds to plant biology. Over 120 million dollars was invested in this beautiful new facility which will house over 100 plant biologists. The Gates Foundation program to eradicate wheat rust disease has also enticed new minds to tackle critical problems in plant and food biology. The Howard Hughes Medical Institute recently recognized the importance of plant biology by endowing a new series of 13 investigators in plant biology (to go with the previous 300 HHMI investigators in biomedical sciences).

But until most major universities fund their plant programs to the level that they fund other departments, until the biology programs at the major universities place plant biology on par with human biology, until plant physiology and ecology are required parts of all biology curricula, then we will not succeed in attracting the top tier of students necessary to tackle the major problems of food security simply because most of these students will continue to see plant biology as secondary to animal biology.

The other 98 questions were of course also important and interesting, and I’d like to share just one more. Question # 48: “How do plants communicate with each other?” For more on that, preorder a copy of my forthcoming book, WHAT A PLANT KNOWS!