Define Epigeal and Hypogeal

John C. MacGregor
Mon, 04 Jan 2010 13:23:38 PST
The meanings of "epigeal" and "hypogeal" are clear from the  
etymology.  They are from the Greek, "epi" = above, on top of, and  
"hypo" = below, and "geios" = earth, ground.  Different disciplines  
apply the terms differently to their specific subject matter.

The Collegiate Dictionary of Botany (Delbert Swartz, Ronald Press,  
1971) gives the following definitions:

epigeal  Germinating with the cotyledons appearing above the surface  
of the ground.

hypogeal Germinating with cotyledons remaining in the seed or under  
the ground,

Strictly speaking, it would depend on where the seed germinated.   
Even larger seeds germinate above ground in wet weather.    But above  
or below, upon germination, geotropism usually sends the radicle  
downward and the shoot bearing the cotyledons upward.

Applied to geophytes, the distinction is between species that  
immediately send a shoot upward to reach the light and those that  
only send out a radicle at first and develop an underground bulb or  
tuber before sending up a shoot.  Often, this is a mechanism to  
prevent browsing of the new growth or burning off by wildfire before  
the plant has enough strength to become established.

John C. MacGregor
South Pasadena, CA, USA
USDA Zone 9
Sunset Zones 21/23

On Jan 4, 2010, at 12:39 PM, J.E. Shields wrote:

> Hi sll,
> "Germination" seems clear enough -- when the embryo starts to elongate
> along its axis and proceeds to grow out of the seed.
> Here is definition of "germination" in
> "The stage in which a germ or a living thing starts to sprout, grow  
> and
> develop. ...
> Germination in plants is the process by which a dormant seed begins to
> sprout and grow into a seedling under the right growing conditions."
> Jim McKenny has it right -- applying the general definition to  
> specific
> cases forces  modifications to fit circumstances.  How to twist the  
> dicot
> definitions of epigeal and hypogeal to fit monocots is the task at  
> hand.
> People do tend to confuse the first above-ground appearance of a green
> shoot with germination of a seed.  This is not a correct technical  
> use of
> the term "germination."  For seeds that germinate above ground or  
> in petri
> dishes, the first appearance of the (white) radicle through the  
> seed coat
> corresponds to true germination.  The same thing applies to  
> germination
> below the surface of the ground.
> Jim Shields
> At 11:58 AM 1/4/2010 -0800, you wrote:
>> The problem is the inclusion of 'germination'. The definition of  
>> hypogeal
>> and epigeal is clear.
>>  T
>>> Date: Mon, 4 Jan 2010 14:51:09 -0500
>>> To:
>>> From:
>>> Subject: Re: [pbs] Define Epigeal and Hypogeal
>>> The problem with the simple definition -- cotyledons above ground  
>>> after
>>> germination vs. cotyledons below ground -- is that for many  
>>> monocots, the
>>> cotyledon stays inside the endosperm structure and that is where  
>>> the seed
>>> was -- above ground or buried, happenstance perhaps -- when the seed
>>> germinated.
> *************************************************
> Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
> P.O. Box 92              WWW:
> Westfield, Indiana 46074, USA
> Tel. ++1-317-867-3344     or      toll-free 1-866-449-3344 in USA
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