A Question About Plant Growth

Editor,

I have a question for your readers. Trees seem to have an uncanny ability to send out branches only where there is open space. They seem to know if there is available space to expand into. If two trees are close together they will branch away from each other and restrict their growth in the direction of the adjacent tree. Yet they will expand greatly in the direction away from their  neighbor.  

Also the branches they send out never touch each other.   

How is this done? 

I  fully understand that direction of growth is due largely to gravity and  light and while I agree that this has a strong influence it seems to me that some other means must be present. To me it seems that both gravity and light are too homogenous to contain data on close by obstructions.   

Allan Rydberg

The phototropic response of plants to blue light is exceedingly sensitive. For example, each spring plants growing under the wood platform from where I do daily sunlight measurements manage to find and grow up through the very narrow slits between the wood planks. In the nearby woods, branches of shrubs and trees often come in contact with one another as they grow toward light penetrating the canopy. Editor.

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The Citizen Scientist (04 June 2010).