The Four Idols

Propagation

Propagation, the act of producing a new plant from a parent plant happens in various ways, the most common of these is by setting seeds.  Propagation can also be effected by bits of the parent plant breaking off and making new plants.

Two trees that self propagate in unusual ways are the Mangrove and the Banyan.  The Banyan, a species of fig, by developing accessory trunks which allow the tree to spread outward indefinitely, and the Mangrove by dropping already germinated seeds into the sea. 

Mangroves grow in harsh coastal conditions that other plants could not tolerate.  Living in saline conditions, ranging from brackish water through pure seawater to water concentrated by evaporation to twice the salinity of ocean seawater, they are specially adapted to take in extra oxygen and remove salt.  The Mangrove’s adaption to oxygen deprivation is by means of lenticels in the bark and also by aerial roots (pneumataphores) which stick out of the ground like straws for breathing, these aerial roots also absorb gases iron and other nutrients which are stored directly in the root system.  The seeds of this remarkable tree are viviparous, this means that they germinate whist still attached to the mother tree.  The seeds drop from the tree into the water where they develop and grow, adding to the density of the coastal grove, or float away on the wind and current.  They drift across the ocean lying in a horizontal position and when they arrive at a suitable beach they change their buoyancy and become vertical so that their root is in the correct position to grow.  If they don’t take root they turn themselves horizontally again and float off to find a more suitable home!

The Banyan has a very different solution to propagation.  It is a type of fig tree the fruit of which are pollinated by their own specific species of wasp which breeds inside the fruit. The fruit are then eaten by frugivore birds who disperse the seeds. The seeds are so small that if they are deposited on the forest floor they are unlikely to germinate because of lack of light.  However many seeds end up on trees, branches and other structures, such as buildings.  When they then germinate they send roots down towards the ground and envelope part of the host tree or edifice.  This is known as a strangler habit.  Seeds that germinate on extended branches can send roots down to the ground, develop into trunks and expand the footprint of the tree.  A cunning way of self propagation!  The strangler habit of the Banyan (and some other figs) is as weird as its name suggests.  As the tree ages, the mesh of roots growing around the original tree can eventually apply huge pressure and kill the original tree.  This leaves a dense forest of trees with a hollow centre, a wonderful haven for wildlife.  The Great Banyan tree of India grows outside Kolcatta (Calcutta), it has over 3600 supplementary trunks and covers 4.7 acres.

It is amazing the complex and difficult methods some plants go through to ensure the propagation of their species.  Although we know that they have no central nervous system or the same understanding of the world as some animals have, there does seem to be a level of decision making going on that we are slow to acknowledge.