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)!