Friday puzzle answer(s)

Wow!  What a lot of great brainstorming over the weekend!  I would venture to say that The Garden Professors have the smartest students in the world.

On to the answer…or answers.  First, the phenomenon.  It’s called paraheliotropism – literally, a movement to protect (the leaves) from the sun (yes, Trena, it is a tropism!). This is the opposite of another phenomenon called heliotropism, or solar tracking.  Sunflowers famously do this, as do a number of arctic species that collect solar warmth for the benefit of their pollinators.  (An aside:  if you have never watched David Attenborough’s The Private Life of Plants you must add it to your Netflix queue.  Right now.)   

But our saxifrage (thanks, Holly! I’m such a taxonomy imbecile) is reducing solar exposure by positioning its leaves in parallel to the sun’s rays.  This is a reversible movement and helps reduce photooxidative stress, leaf temperature, and water loss.  It’s an important strategy as the newly emerging leaves are actively expanding.  If turgor is reduced by high temperature or water loss, so is the final size of the leaf. 

Finally, these rapidly expanding leaves have relatively thin cuticles (if they were thicker the leaves wouldn’t be able to expand as well).  The cuticle gives further protection to the leaf from water loss due to heat, drought, wind, or even late season freezing events (thanks for that addition, John!).  The cuticle will mature after the leaf has reached its full size.

So, as Foy suggested, this is a way for leaves to "harden off" and reach full size before exposing themselves to the sun.  Aren’t plants cool?

And you are all such great participants!  Group hug!  Now, back to work.

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

2 thoughts on “Friday puzzle answer(s)”

  1. Thanks for the kind words, Foy! All four of us enjoy working with people, and as you point out, it’s important to listen as well as talk. A dynamic, engaged blogging community is much more interesting than us just droning on and on…

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