Subject: Re: Old Wives, water droplets was FROST

Jonathan Knisely
Wed, 14 Nov 2007 07:35:23 PST
Message: 10
Date: Wed, 14 Nov 2007 07:22:44 -0800 (PST)
From: Robt R Pries <>
Subject: Re: [pbs] Old Wives, water droplets was FROST
To: Pacific Bulb Society <>
Message-ID: <>
Content-Type: text/plain; charset=iso-8859-1

 I some of the posts there was speculation about water
droplets focussing sumlight and causing damage. As I
remember the old wives tales; their concern was about
water droplets setting on leaves in the middle of the
day in Spring or summer. I guess I need to verify that
with my wife. I believe there was also a warning that
water droplets should not set on leaves of African
Violets if the sun is coming through the window. I
sort of understand the last tale since African Violets
(Santipaulia)growing in a window on a winters day may
suffer chill damage from the rapid evaporation of a
water droplet as the sun hits it. Sunlight is directly
related to evaporation rates. This is how they
discovered that less sunlight strikes the ground today
then 50 years ago because evaporation rates have
fallen. The sun is still puting out the same amount of
light but the polution in the atmosphere now reflects
as much as 20% back to space before it gets to the
earth. I have wondered if this is having an effort on
plants that require high light intensity for growth.
But back to the water droplets. I don't remember any
wives tales that talk about water droplets focusing
light in winter.


I always assumed that the water droplet, kept above the surface of the leaf by the leaf hairs of the saintpaulia, would then be able to act as a lens and focus light onto the leaf.  Just like a magnifying glass.  

It doesn't really make sense, as I think about it, and I suspect you'll agree, that the sun's heat would lead to increased chilling of the leaf under where the waterdrop was located--it wouldn't evaporate any more rapidly than the sun's heat caused it to vaporize.

Jonathan Knisely
Coastal Connecticut, USDA 6a

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