In line with our ‘make love, not war’ mentality, we currently have no plans to weaponise RoboPlant. If, however the MoD were to commission us to make a ‘combat version’, we would probably replace some of its leaves with rocket launcher modules, which would fire hydrogen-powered rockets (oh, the beauty of modularity!).
When I say hydrogen-powered rockets, do not get confused with NASA’s space rockets mentioned in the previous article (see ‘Will hydrogen power the future?’). However, the same principle of reaction energy applies with small-scale bottle rockets. The electrolyser would feed hydrogen and oxygen into a bottle rocket mounted on a launcher module. The rocket is filled with water, which is displaced by the gases and allowed to leak out. Once a sufficient amount of oxygen and hydrogen has filled the rocket, it can be ignited with a fuse mounted on the launcher. The ignition of the gases results in an explosion, the pressure of which blasts the rocket forth. We saw one of these rockets on out visit to the Magna Science Centre, with an electrolyser powered by a hand-operated dynamo. If RoboPlant were to have rocket launchers, there would be no need for a dynamo as the power is supplied by photovoltaic cells.Although it sounds a bit ridiculous, this wouldn’t be entirely inaccurate in regards to the machine-plant analogy. In nature, plants have to defend themselves in some way, to prevent them being completely obliterated by grazing animals. There are many defence strategies plants can employ, including structural and chemical defences, as well as some more devious tricks.
Structural defences are the simplest means of deterring grazers. If you’re one of those people who likes to venture outdoors once in a while, you’ve probably pricked yourself on thorn bushes a few times. Now imagine you’re a grazing animal. Would you eat that plant? No, you wouldn’t, and thus sharp bits provide an excellent example of an anti-herbivore defence mechanism. There are actually three kinds of structures which serve this purpose, distinguished by the basic part of the plant’s anatomy which is used to make them. Thorns are modified from branches – imagine evolution took a pencil sharpener to the branches of a plant. Spines are modified from leaves, while prickles are modified from hair-like structures. Whichever part of the plant’s anatomy sharp bits are derived from, they often end up being pretty similar anyway, and usually have the same painful result. Cacti are an extreme example, as they often cover themselves entirely with sharp spines to protect the precious water which they may have spent years collecting.What’s worse than pricking yourself on a thorn? Getting stung by stinging nettles. You should know from experience that the pain of nettles persists for quite some time after initial contact. This is because the leaves of a stinging nettle are lined with hollow hairs which inject several chemicals which play nightmares with the nerves under your skin. This is just one example of a chemical defence mechanism. Other plants produce chemicals to give themselves a bitter taste, so herbivores will be put off after the first bite, while others produce chemicals that are poisonous and can make animals sick, or worse. A sick herbivore is a vulnerable one, so natural selection acts in favour of animals which leave plants like Rhododendron out of their diet.
Some plants can be a little more cunning, by using other species to their advantage. For example, Acacia plants are home to colonies of large, biting ants. The ants fight tooth and nail to defend their home, which means tearing invading beetles to shreds, and biting and stinging the faces of any herbivores brave or foolish enough to come within range. Studies have also identified some plants which release special chemicals which attract predators to herbivores feeding on them. The concept that “the enemy of my enemy is my friend”, it seems, is quite prevalent in nature.Here, I’ve given a brief overview of some of the different kinds of plant defence mechanisms, but there are many more that you can find out about. Despite the diversity of defence mechanisms in the plant kingdom though, no species which shoot rockets have been identified (yet). Perhaps mounting rocket launchers on RoboPlant would not serve as the best analogy, then, but maybe lining the leaves with hypodermic needles would work better…