Tuesday, August 1, 2017

Plant physiology: Wonder how water reaches the top of trees.

In memory of my professor and thesis adviser, 
Dr Fernando de Peralta
Dr Abe V Rotor
Article inspired by a scientific study -  The theory of the rise of sap in trees : some historical and conceptual remarks by Harvey R. Brown, Faculty of Philosophy, University of Oxford Radcliffe Humanities, Radcliffe Observatory Quarter Woodstock Road, Oxford OX2 6GG, U.K. 
                    Top: Liana climbs on the trunk of a twenty-foot tall betel nut. 
                     Philodendron clings on the trunk of a thirty-foot mango tree.   
                  Photos by the author at his residence in San Vicente, Ilocos Sur.

Draw water from a well with a bucket with rope and pull it up with bare hands.
Carry the bucketful of water over a flight of stairs, two to more storeys high;

Draw out ground water with a surface pump but only up to a certain depth.
At sea level, you could only pump water from a depth of just under 34 ft or 10.3m.

When sipping with straw, the smaller its diameter the lesser effort you need.
The "fatter" the straw the more effort you need, then you can no longer succeed.

Notice sandy soil does not retain as much water as clayey soil does, why is it so?
It's the Principle of Capillarity: water rises higher through smaller soil inter-spaces.

Examine a longitudinal section of wood and you will find a series of "tubes"
interconnected laterally and longitudinally, collectively a capillary complex.

When air is humid, clothes get damp, bread soggy, wood moist, paper soft;

they are hygroscopic: water molecules bind tenaciously with these materials. 

In ancient times, blocks of rocks were cut by driving wood wedges into the cracks.
Water is poured over the wood wedges which expand and dislodge the blocks.

The principle involved in the wick of a kerosene lamp to keep the light steady -
demonstrates molecular cohesion of fuel, and adhesion of fuel and wick.

Water rising to the top of trees and lianas clinging on them is a combination
these principles - and theories - yet no full explanation can solve this mystery.


Here is a study to serve as reference in Plant Physiology a three-unit major subject in Botany.  

The theory of the rise of sap in trees: some historical and conceptual remarks 

Harvey R. Brown Faculty of Philosophy, University of Oxford Radcliffe Humanities, Radcliffe Observatory Quarter Woodstock Road, Oxford OX2 6GG, U.K. harvey.brown@philosophy.ox.ac.uk 


The ability of trees to suck water from roots to leaves, sometimes to heights of over a hundred meters, is remarkable given the absence of any mechanical pump. This study deals with a number of issues, of both an historical and conceptual nature, in the orthodox “Cohesion-Tension” theory of the ascent of sap in trees. The theory relies chiefly on the exceptional cohesive and adhesive properties of water, the structural properties of trees, and the role of evaporation (“transpiration”) from leaves. But it is not the whole story. Plant scientists have been aware since the inception of the theory in the late 19th century that further processes are at work in order to prime the trees, the main such process – growth itself – being so obvious to them that it is often omitted from the story. Other factors depend largely on the type of tree, and are not always fully understood. For physicists, in particular, it may be helpful to see the fuller picture, which is what this study attempts to provide in non-technical terms.

“There are therefore agents in Nature able to make the particles of bodies stick together by very strong attractions. And it is the business of experimental philosophy to find them out.” Isaac Newton

“To believe that columns of water should hang in the tracheals like solid bodies, and should, like them, transmit downwards the pull exerted on them at their upper ends by the transpiring leaves, is to some of us equivalent to believing in ropes of sand.” Francis Darwin

“Water is unique in its importance and its properties. No other substance has been the subject of so much study and speculation, nor has any been harder to understand at a molecular level.” J.S. Rowlinson 

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