Mayapples...They Aren’t Really Apples ©

 

 

Mayapple, podophyllum peltatum, picture by the Author.

If you have ever wandered through the spring or early summer woods of the eastern half of the United States and Canada, then you have probably seen mayapples, podophyllum peltatum, springing up from the ground in the moist areas under deciduous trees...but they aren’t really apples.  In fact, except for the ripened berry, all other parts of the plant, the stems, roots, unripe berries, and the seeds in the berry, all contain podophyllotoxin, an alkaloid, that is highly poisonous!

 

Mayapples, podophyllum peltatum

 

A painting by Charles Frederick Millspaugh, 1887, in American Medicinal Plants, from Wikimedia, HERE.

Mayapples are also known as indian apples, american mandrake, wild mandrake, or pomme de mai, and even though it is a highly poisonous plant, it has been used for centuries as a cathartic medical tonic to purge a patient and relieve constipation and induce vomiting¹, and the ripe berries, which is the only part of the plant that is not poisonous, with the poisonous seeds removed, have been eaten or made into jams or pies² for just as long.

 

An excerpt from Medicine in Virginia in the eighteenth century, by Wyndham B. Blanton, M.D., page 216.

The mayapple, podophyllum peltatum, is a common and widespread herbaceous perennial plant that is native across much of eastern North America, growing in colonies from a single root, in open deciduous forests, shady fields, roadsides, and riverbanks.  Just as with many other native wildflowers, mayapples sprout early in the spring, before the surrounding trees develop leaves, and then the stems and leaves wither and die by mid-summer.

 

Mayapple, podophyllum peltatum, distribution, from “Podophyllum peltatum L.”, by Natural Resource Conservation Service.

The upright stems all grow from a single, branched root, which is made up of many thick, dark to reddish brown tubers connected by fleshy, fibrous tendrils and downward spreading roots.  Each terminal bud on the roots produces a single shoot which will develop into a 12-18 inch (30-45 cm) tall stem, with one or two umbrella-like (peltate) leaves, having between five and nine lobes.

 

A mayapple, podophyllum peltatum, photograph by the Author.

Mayapples are called mayapples, because they flower in April or May, and because the flowers look like apple blossoms.  Only stems with two leaf stalks will have a single flower, which will bud from the axil, where the two leaves attach to the stalk.  Each blossom is about two to three inches (5-8 cm) across and is white to rose-colored with six to nine waxy petals.  The flowers are quite pretty, but they are often hard to find as they are hidden under the leaves and are short lived.

 

“Flower from the Mayapple (Podophyllum peltatum)”, by Willthomas, from Wikimedia, HERE.

The pollinated flower produces a green, lemon-shaped berry, containing several tan seeds.  These 1-½ to 2 inch (4-5 cm) long berries turn to a golden, yellow color, sometimes tinged with pink or purple by late summer.  The ripened berries (but not the seeds) are edible and can be used in preserves or pies. 

 

“Botanical model of Podophyllum peltatum by George and Paul Marchand in the Buffalo Museum of Science, Buffalo, New York, USA”, by Daderot, from Wikimedia, HERE.

So next time you are walking in the early spring to late summer woods of eastern North America, and you see large umbrella like leaves sprouting under the trees, you’ll know that they are mayapples, which aren’t really apples at all!

 

Don’t forget to come back next week and read “Dry Gripes, Lead Poisoning and Mayapples©”, where we will talk about on the historical, medical uses of mayapples and a common 18^th century ailment, which was actually a symptom of lead poisoning!

 

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at BandanaMan Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

That is all for now, and as always, until next time, Happy Trails!

 

 

Notes

 

¹ For more information on the historical, medical uses of mayapples, look for a future article entitled “Dry Gripes, Lead Poisoning and Mayapples©”

 

² For more information on making mayapple jams or pies, become a Patreon subscriber and look for a future article entitled “Cooking with Mayapples©”

 

Sources

 

Blanton, Wyndham B., M.D.; Medicine in Virginia in the eighteenth century, [Richmond, Garrett & Massie, Inc., 1931], page 216, https://catalog.hathitrust.org/Record/001557339, accessed June 21, 2022

 

Elias, Thomas S. and Dykeman, Peter A.; Field Guide To North American Edible Wild Plants, [Outdoor Life Books, Times Mirror Magazines, Inc., New York, NY, 1982], pages 140 and 262.

 

Mahr, Susan; “Mayapple, Podophyllum peltatum”, [© 2022 The Board of Regents of the University of Wisconsin System, University of Wisconsin – Madison], https://hort.extension.wisc.edu/articles/mayapple-podophyllum-peltatum/, accessed June 12, 2022

 

Natural Resource Conservation Service; “Podophyllum peltatum L.”, [United States Department of Agriculture], https://adminplants.sc.egov.usda.gov/java/profile?symbol=POPE, accessed June 12, 2022

 

Wikimedia, “American_medicinal_plants;_an_illustrated_and_descriptive_guide_to_the_American_plants_used_as_homopathic_remedies-_their_history,_preparation,_chemist”, by Charles Frederick Millspaugh, 1887, https://commons.wikimedia.org/wiki/File:American_medicinal_plants;_an_illustrated_and_descriptive_guide_to_the_American_plants_used_as_homopathic_remedies-_their_history,_preparation,_chemistry_and_physiological_effects_(1887)_(17534042604).jpg, accessed June 21, 2022

 

Wikimedia, “Botanical model of Podophyllum peltatum by George and Paul Marchand in the Buffalo Museum of Science, Buffalo, New York, USA”, by Daderot, January 20, 2010; https://commons.wikimedia.org/wiki/File:Marchand_models_in_Buffalo_Museum_of_Science_-_IMG_3839.JPG, accessed June 21, 2022

 

Wikimedia, “Flower from the Mayapple (Podophyllum peltatum)”, by Willthomas, April 26, 2021, https://commons.wikimedia.org/wiki/File:Podophyllum_peltatum_flower.jpg, accessed June 21, 2022,

 

Hypothermia, It Can Happen Any Time, Anywhere ©

 

 

Cold, wet, rain, hypothermia weather.  Taken in Snohomish County, Washington”, by pfly, from Wikimedia, HERE.

If you are like most people, you probably consider hypothermia as something to only worry about in the depths of winter, when it is freezing cold outside.  But you would be wrong!

 

Hypothermia means “low heat” and it can happen anytime you lose your core body heat faster than you can replace it.  It can strike anytime, anywhere, indoors, or out, even in relatively warm 50^oF (10^oC) temperatures!  And while hypothermia is common in the winter, according to Princeton University it actually occurs most often during the spring and fall¹ and can occur also in the summer.  Unfortunately, prominent Seattle hiking expert Karen Sykes, who was 70 years old, died of hypothermia on June 18, 2014, while hiking the Owyhigh Lakes Trail in Mount Rainier National Park which has a maximum elevation of 5,272 feet (1,607 m)².

 

Hypothermia is defined as a cooling of the body’s core temperature to below 95^oF (35^oC) and is often caused by a combination of three factors, cold or quickly changing temperatures, strong winds, or being wet, either from rain, sweat or being immersed in cold water.  Four other factors that contribute to hypothermia are high elevations, which can experience quickly changing wind and weather; age, because the very young and the old have a harder time regulating and maintaining their body heat; dehydration, which decreases your body’s ability to regulate its thermostat; and fatigue or exhaustion, because low energy means you have less to burn to keep you warm. 

 

How you lose heat...

 

“Illustration of the basic methods heat loss”, by Baedr-9439, February 25, 2020, modified by the Author with material from A Pocket Guide to Cold Water Survival, by the Coast Guard .  Original from Wikimedia, HERE.

Your body loses heat through four processes, convection, conduction, radiation, and evaporation.

 

Convection or wind chill can cool you very quickly.  Alan E. Course, in The Best About Backpacking, wrote “a two-mile-an-hour breeze can drag down body temperature as effectively as a twenty-mile gale if the victim’s clothes are wet”.  Your body will lose between 10% to 15% of its heat through convection.

 

You lose body heat by conduction to the ground, if you are sitting or sleeping on snow or the ground, to the air around you, or to water if you are swimming or immersed in it.  Body heat is lost to the air at temperatures lower than 68°F (20°C), and your body will lose about 2% of its heat by air conduction.  However, you lose body heat to water about 25 times faster than to the air, so you can lose body heat very quickly if you are in cold water or wearing wet clothing.

 

Radiation is the process of heat moving away from your body, like heat leaving a hot stove, and usually occurs in air temperatures lower than 68°F (20°C).  The body loses 65% of its heat through radiation.

 

You will lose body heat by evaporation of water from your skin if you are sweating, or from your clothing if it is wet.  During heavy exercise, your body will shed 85% of its heat by sweating.  Also, you lose some body heat through respiration (breathing).  Heat loss by evaporation and respiration will increase in dry or windy conditions.

 

What is Hypothermia...

 

From A Pocket Guide to Cold Water Survival, by the Coast Guard, page 7.

Hypothermia is the lowering of your body’s core temperature to 95^oF (35^oC) or below and has three stages, mild, moderate, and severe. 

 

Mild Hypothermia is when your core body temperature falls from 98.6^o (37^oC) to between 95^o and 90^oF (35^o to 32^oC).  The symptoms of mild hypothermia are intense, but controllable shivering and cold numb hands or the “fumbles”³. 

 

Moderate Hypothermia is when your core body temperature falls from 90^o to 86^oF (32^o to 30^oC).  The symptoms of moderate hypothermia are uncontrollable shivering, confusion and movements that become slow and labored, and slurred speech -- look for the “stumbles”, the “mumbles”, and the “grumbles”.

 

Severe Hypothermia is when your core body temperature drops to between 86^o and 78^oF (30^o to 25^oC).  The symptoms are extremely cold skin, sleepiness or unconsciousness and a pulse that is irregular or difficult to find.

 

Stay at 98.6^o...

 

Stay at 98.6^o, an excerpt from A Pocket Guide to Cold Water Survival, by the Coast Guard, page 2.

There are five things that you need to do to keep yourself at 98.6^oF (37^oC), and to avoid hypothermia: dress in layers, stay dry and keep “comfortably cold”, stay hydrated, eat often, and be prepared.

 

Stay warm.  Always dress in layers, because the layers will help trap your body heat close to your skin and will prevent the wind and the wet from stealing it away.  Wear an inner layer of synthetic weave to wick away the sweat, a middle layer of synthetic, down or wool to provide insulation and an outer waterproof/windproof layer to break the wind.  And always take a knit hat, a knit hat is essential because heat loss from your bare head can be 50% at 40^oF (4^oC) and 75% at 5^oF (-15^oC).  Bringing extra dry clothes in case you get wet or an extra insulative layer in case the temperature drops is also, always a good idea.

 

From A Pocket Guide to Cold Water Survival, by the Coast Guard, page 6.

Stay dry!  If it is wet out, put on your waterproof layers or take shelter.  And stay “comfortably cold” by taking off your insulative layers or your knit hat as you become too warm, because as Les Stroud, The Survivorman says, “You Sweat You Die”! 

 

From A Pocket Guide to Cold Water Survival, by the Coast Guard, page 12.

Stay hydrated and stay fed.  Even low levels of dehydration of less than a 2% loss of body weight⁴, can lower your blood volume and affect your circulation and your body’s ability to regulate its thermostat, this can result in hypothermia.  Also, your body uses food as energy and it takes energy to make heat, so, when it is cold, you must eat more often.  But remember you need to have water to digest your food, so if you don’t have water, don’t eat.

 

Be prepared.  Always dress for the worst weather you might experience, your first line of defense against the cold and the wet, are the clothes you are wearing and the extra clothes that you have with you.  Especially during the spring, summer and fall, travelers in the wilderness often do not bring enough, or bring the right kinds of clothes.  And always, bring a tent, a tarp, or some way of making an emergency shelter with you, when you go out in the wilderness.  If a storm blows up make camp right away, because setting up camp takes time and energy, and if you are cold, you might not have much of either.  Personally, I always carry two heavy grade, 55-60 Gallon, 3.0 Mil, 38"W x 58"H, contractor trash bags, in case I have to make an emergency trash bag shelter (for more see “Using your poncho or a trash bag as an Emergency Shelter ©”, HERE, or for a video, go HERE).  

 

So, be safe, keep warm and dry and stay at 98.6^oF, spring, summer, fall, or winter!

 

Don’t forget to come back next week and read “Mayapples...They Aren’t Really Apples ©”, where we will talk about a common woodland flowering plant that really isn’t a what it is called, and which appears during the spring and disappears by mid-summer.

 

 

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at BandanaMan Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

That is all for now, and as always, until next time, Happy Trails!

 

 

Notes

 

¹ “Cold Stress Facts”, Environmental Health and Safety, Princeton University

 

² From Eric M. Johnson, “Seattle hiking expert Sykes died of hypothermia: official” and Pro Trails, “Owyhigh Lakes - 7.0 miles”.

 

³ Watch out for the “umbles”: the fumbles, a sign of cold numb hands and mild hypothermia, and the mumbles, stumbles, and grumbles, a sign of confusion and slowed thinking and movement, all of which are symptoms of moderate hypothermia.

 

The best field test for early or mild hypothermia, is to ask the person to walk in a straight line, if they are unable to walk 20 to 30 feet (6 to 9 m) in a straight line, they might be hypothermic.

 

From “Warning Signs of Hypothermia: Know Your ‘Umbles’”, by Matt Heid.

 

 

⁴ From “Dehydration, Hyperthermia, and Athletes: Science and Practice”, by Robert Murray, PhD.

 

 

Sources

 

Coast Guard, Department of Transportation, A Pocket Guide to Cold Water Survival, CG 473, September 1975, https://books.googleusercontent.com/books/content?req=AKW5QafxNJBmiIml6O4jiudRpr2rz8pLfodQOiq-4gZNh4xa5uIN_rq05C2yAes1AYw67Ziq189QaQaFDHBHE0SJivfCxjMW1DReANLjFqw1qX6jEl2mz1HPKXj4BRQJv8zAOcO6oDE70Dcv__VE2uPh4tEqLSzMxDRiWOv3p6ssyQjE2bevJMX7-Ol2KDtIPQVcVuaJudJMLaOOuSUVs8qYS1Nlaxnm47GVOCXLR79KzL6nV3R0zZG4DxRt9hoYrIRGugXm6RVfbU2gxeix7JLKbxpvQsNB9w, accessed May 1, 2022

 

Environmental Health and Safety, “Cold Stress Facts”, [© 2022 The Trustees of Princeton University], https://ehs.princeton.edu/workplace-construction/occupational-health/heat-cold-stress/cold-stress-facts, accessed June 14, 2022

 

Heid, Matt; “Warning Signs of Hypothermia: Know Your ‘Umbles’”, February 11, 2014, [© 2022 Appalachian Mtn Club], https://www.outdoors.org/resources/amc-outdoors/health-and-safety/warning-signs-of-hypothermia-know-your/, accessed June 18, 2022

 

Johnson, Eric M.; “Seattle hiking expert Sykes died of hypothermia: official”, June 24, 2014, [© 2022 Reuters], https://www.reuters.com/article/us-usa-hiker-washington/seattle-hiking-expert-sykes-died-of-hypothermia-official-idUSKBN0EZ0OQ20140624, accessed June 14, 2022

 

Murray, Robert, PhD.; “Dehydration, Hyperthermia, and Athletes: Science and Practice”, Journal of Athletic Training, July-September 1996, 31(3), pages 248–252, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1318513/, accessed June 18, 2022

 

MyHealth.Alberta.ca, “Cold Exposure: Ways the Body Loses Heat”, [© 2022 Government of Alberta], https://myhealth.alberta.ca/Health/pages/conditions.aspx?hwid=tw9037#:~:text=Convection%20(similar%20to%20sitting%20in,of%20its%20heat%20through%20convection., accessed June 18, 2022

 

Pro Trails, “Owyhigh Lakes - 7.0 miles”,[ © 2021 ProTrails], https://www.protrails.com/trail/851/mount-rainier-national-park-owyhigh-lakes, accessed June 18, 2022

 

Van Lear, Denise; The Best About Backpacking, [Sierra Club, San Francisco, 1974], page 355

 

Wikimedia; “Cold, wet, rain.  Taken in Snohomish County, Washington”, by pfly, November 12, 2007, https://commons.wikimedia.org/wiki/File:Rain_shower_after_cold_front_3.JPG, accessed June 10, 2022

 

Wikimedia; “Illustration of the basic methods heat loss”, by Baedr-9439, February 25, 2020, https://commons.wikimedia.org/wiki/File:Mechanisms-of-heat-loss.png, accessed June 17, 2022

 

Weather for Woodsmen, Beaufort’s Scale and Estimating Wind Speed by Observation ©

 

 

So just how fast was the wind blowing?  Do you know?  Photograph by the Author, taken  on August 27, 2020.

 

The third in a series of articles on weather for woodsmen, for the previous article, go HERE – Author’s Note

Can you estimate how fast the wind is blowing from the things you see around you?  If so, how fast is the wind blowing in the picture above, do you know?  And is it important to know how strong the wind is blowing anyways?

 

Mankind has been studying the weather and observing the winds and their effects on the land and the sea for the last 200,000 years, but it wasn’t until Francis Beaufort designed the scale bears his name that the study and description of winds was organized and classified¹. 

 

The original Beaufort scale, from “Beaufort scale of wind force as adapted for use on forested areas of the northern Rocky Mountains”, by George M. Jemison, page 77.

And according to Francis Beaufort, and the other meteorologists who have revised and updated his scale over the following two centuries, you can estimate the speed of the wind by observing its effects on the land and sea that it blows upon.  In 1960, Beaufort’s scale of wind force reached its modern form, when probable wave heights and probable maximum wave heights were added.  Probable wave height refers to the height of waves experienced far from land in the open sea, remember waves build as they approach shore, because drag from the bottom slows the wave and when that happens the waves get closer together and taller.  And the probable maximum wave height is the height of the highest wave that can be expected in a 10-minute period².

 

A modern example of Beaufort’s Scale, from Sailing: A Beginner's Guide, by David Seidman.

So, you can estimate the speed of the wind by observing its effects on the land and sea that it blows upon.  But is it important to know the wind speed?  Yes, there are several situations where knowing the wind speed is helpful, such as when you are travelling by boat over large bodies of water or when you are travelling where dust or snow could be blown around reducing visibility, however there is one instance where knowing the wind speed is crucial and that is when there is a possibility of wind chill and hypothermia!

 

“Blow, winds, and crack your cheeks! rage! blow!”

William Shakespeare, King Lear, Act III, Scene II

 

An excerpt from "Historia de gentibus septentrionalibus", 1555, by Olaus Magnus, from Wikimedia, HERE.

Knowing the wind speed allows you calculate the wind chill, which is the combined effect of the air temperature and wind speed.  The wind chill is always less than the actual air temperature and knowing what it is allows you to determine how long you can safely be out in the weather without risking frostbite or hypothermia.  Alan E. Nourse, in The Best About Backpacking, wrote “a two-mile-an-hour breeze can drag down body temperature as effectively as a twenty-mile gale if the victim’s clothes are wet”.  And remember hypothermia isn’t just something that happens in the winter, more people die of hypothermia during the spring, summer or fall, than during the winter.

 

NOAA Wind Chill chart.

One way to estimate the wind speed is to watch a flag and use math.  When looking at a flag, estimate the angle of the flag compared to the flagpole and take the angle of the flag and divide it by the number four.  The answer will give you the wind speed in miles per hour³.

 

ANGLE OF FLAG / 4 = WIND SPEED in MPH

 

·       If the flag is not moving and down on the pole, or if it only occasionally stirs, then the wind is calm.  On the chart below the wind would be class 0 if the flag is down and class 1 if only occasionally stirs.

 

·       If the flag is extended at 45^o, then wind is about 11 mph (about 18 kph), and on the chart below the wind would be class 3.

 

·       If the flag flaps lightly and is more than 45^o but less than a fully extended 90^o, then wind speed is between 12 to 18 mph (between 19-29 kph), and on the chart below the wind would be class 4.

 

·       If the flag is fully extended to 90^o and waving over its entire length, the wind speed is between 19 to 24 mph (between 30-39 kph), and on the chart below the wind would be class 5.

 

·       If the flag is stretched and flapping fast, the wind speed is between 25 to 31 mph (40-50 kph), and on the chart below the wind would be class 6.

 

·       If the flag is stretched and flapping hard, the wind speed is between 32 to 37 mph (51-59 kph), and on the chart below the wind would be class 7.

 

However, the easiest way to estimate the wind speed in the field is to look at a flag or, you can use the movements of the trees, bushes, and grass, and compare what you see to the chart below.

 

Excerpts from George Jemison’s Tables 2 and 3, and from Sailing: A Beginner's Guide, by David Seidman, combined into one chart.  Graphic by the Author.

 

So, know you know how to estimate wind speeds.  By looking again at the front picture and the chart above, can you estimate how fast the wind was blowing?  To find out the answer go to note⁴.

 

The break wall on the Buffalo Outer Harbor measures 14 feet (4.3 meters) above the water and the waves on August 27, 2020, which were crashing over it!  Photograph by the Author.

Don’t forget to come back next week and read “Hypothermia!  It can Happen at Any Time, or Anywhere ©”, where we will talk about hypothermia and how stay warm and safe.

 

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at BandanaMan Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

That is all for now, and as always, until next time, Happy Trails!

 

 

Notes

 

¹ Captain Beaufort wasn’t the first to try to classify wind speed, others, such as Daniel Defoe who had created a 12-point scale in 1704 that was very similar to Beaufort’s later scale, had beaten him to it.  However, Beaufort’s scale was the first to gain acceptance and come into general use.

 

From “Beaufort: National Meteorological Library and Archive Fact sheet 6 – The Beaufort Scale”, by the Met Office, page 3.

 

² According to the authors of “Beaufort: National Meteorological Library and Archive Fact sheet 6 – The Beaufort Scale”, “Strictly, it applies only when the sea is fully developed; that is, when waves have reached their maximum height for a particular wind speed.  Care must be exercised when the fetch and duration of the wind are limited (the fetch is the distance over which the wind has blown, and the duration the time it has been blowing).  It is also worth remembering that the appearance of the sea’s surface is influenced not only by wind but also by swell (waves from far away), precipitation, tidal streams and other currents.”

 

Ibid., page 8.

 

³ From Paul Wetzl, “How to use a flag to find the wind speed”.

 

⁴ The wind on August 27, 2020, averaged 17.9 mph (28.8 kph) and at noon when that picture was taken the wind was blowing at an average of 18.1 mph (29.1 kph).  That means it was a class 4, moderate wind.

 

From “World Weather, Weather in Buffalo, August 27”, HERE.

 

 

Sources

 

Jemison, George M.; “Beaufort scale of wind force as adapted for use on forested areas of the northern Rocky Mountains”, Journal of Agricultural Research, Vol. 49, No. 1, July 1, 1934, [Forest Service, United States Department of Agriculture, Washington, D.C.], page 77 to 82, https://www.fs.fed.us/rm/pubs_exp_for/priest_river/exp_for_priest_river_1934_jemison01.pdf, accessed June 5, 2022

 

Met Office; “Beaufort: National Meteorological Library and Archive Fact sheet 6 – The Beaufort Scale”, [Met Office, © 2010], https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/library-and-archive/library/publications/factsheets/factsheet_6-the-beaufort-scale.pdf, accessed June 5, 2022

 

Seidman, David; Sailing: A Beginner's Guide, [A & C Black (Publishers) Ltd, 1995]

 

Van Lear, Denise; The Best About Backpacking, [Sierra Club, San Francisco, 1974], page 355

 

Wetzl, Paul; “How to use a flag to find the wind speed”, Youngstown Weather, May 11, 2021, Updated June 4, 2021, [© 2022 Nexstar Media Inc.], https://www.wkbn.com/weather/weather-for-kids-how-to-use-a-flag-to-find-the-wind-speed/, accessed June 6, 2022