Exercise No. 4
The Endosperm and the Seed
I. INTRODUCTION
The endosperm is formed by the fusion of one of the male gametes with two polar nuclei
during fertilization. It is a storage tissue which provides nutrition for the embryo and the young
seedling. There are three main types of endosperm; Cellular Endosperm, Nuclear Endosperm and
Helobial Endosperm.
A cellular endosperm is one in which the endosperm cell divides mitotically, regularly
followed by cytokinesis. Thus, each endosperm nucleus is contained within a cell wall from the
beginning. A nuclear endosperm is one in which the early mitotic divisions are not followed by
cytokinesis. Thus, numerous nuclei are contained within a single cell, at least early in development;
later, cell walls typically surround the nuclei. A helobial endosperm is one in which the first
mitotic division is followed by cytokinesis, delimiting two cells. However, the nucleus of one cell
continues a nuclear type of development; that of the other cell divides in a cellular fashion
(Simpson, 2010).
Figure 1. The three traditionally recognized endosperm types (Floyd and Friedman, 2000)
The fertilized ovule transforms into seed and increases in size. The integuments become
hard and tough by growing into seed coats, the testa and the tegmen. The bulk of the seed is taken
by nutritive fleshy cotyledons. The embryo consists of an axis, in which one or two cotyledons
are attached. At one end is the rudimentary bud or shoot apex of the embryo known as plumule,
while on the other end is the rudimentary root or the radicle. On the other surface of the seed is a
deep ridge, the raphe. At one end of the raphe is a tiny pore, the micropyle.
When a seed germinates, it will swell, and the radicle will emerge through the micropyle.
At this portion of the axis, above the point of attachments of the cotyledons is the epicotyls and
that below the point of insertion of the cotyledons, is the hypocotyls. At the time of emergence of
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the plumule, if the hypocotyls elongate more rapidly, the cotyledons will be lifted above the ground
and form the first leaves of the seedling. This is the epigeal germination. If it is the epicotyl region
which elongates more rapidly and the cotyledons are left on the ground and the plumule provides
the first leaves of the seedling, then the germination is hypogeal.
A corn grain is a one-seeded fruit, the pericarp of which is fused with the seed coat of the
single large seed. It is composed of the embryo and the endosperm. The embryo consists of a single
cotyledon, the scutellum and the embryo axis. The scutellum is a broad, blade-like absorbent
organ, lying against the endosperm by a sheath of tissue called the coleoptiles and the root by a
similar sheath known as the coleorhizae. The testa of the castor bean seed is hard and brittle while
the tegmen is thin and membranous, enclosing the larger endosperm. There is a white caruncle
which is an outgrowth of the testa. The endosperm occupies the bulk of the seed while the embryo
is small which is enfolded by two thin papery cotyledons. The seed coat of bean is composed of
thick soft testa and membranous tegmen. The embryo consists of two fleshy cotyledons, the
plumule and the radicle.
Figure 2. Seed Morphology (Simpson, 2010)
II. OBJECTIVES:
At the end of the exercise, the students should be able to:
a. identify the parts and functions of the different types of endosperm;
b. familiarize the process of endosperm development; and
c. identify and determine the parts and types of seeds.
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III. MATERIALS:
Dry red or white bean seeds (Vigna radiata)
Germinated red/white bean seeds
Dry corn seeds (Zea mays)
Germinated corn seeds
Castor bean seeds (Ricinus communis)
Mature coconut fruit (Cocos nucifera) cut in half
Magnifying glass/ Hand lens
IV. PROCEDURE:
1. Soak the red or white bean seeds and corn seeds for a minimum of 3 days in water so that the
seeds will germinate.
2. Examine a dry red/white bean seed. Observe the presence of the hilum, micropyle, raphe, testa
and tegmen. Cut open a germinated bean seed and using the magnifying glass/ hand lens,
observe the number of cotyledons present. Did you observe the epicotyls, plumule, hypocotyls
and radicle? Is the endosperm present in the bean seed? Draw and label parts.
3. In a similar manner, examine a dry and germinated corn seed. Note the presence of scutellum,
plumule, coleoptiles, hypocotyls, coleorhizae and radicle. Can you see the endosperm? Draw
and label parts.
4. Likewise, examine a castor bean seed. Observe the texture of the testa and the tegmen. Can you
observe the caruncle, endosperm, cotyledons and plumule? Externally, do you see the raphe,
hilum and micropyle. Draw and label parts.
5. Examine a matured coconut fruit cut in half. Identify parts such as the exocarp, mesocarp,
endocarp, cotyledon, endosperm, and embryo. Determine the type of endosperm present. Draw
and label parts.
NOTE: All answers should be handwritten, and all drawings should be done using a pencil.
Coloring your drawings is optional. Copy pasting answers from the internet is not
allowed.
V. RESULTS AND OBSERVATIONS: Accomplish the DATA SHEET
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REFERENCES:
Bewley, J.D. and M. Black, M. 1994. Seeds: physiology of development and germination. 2nd
ed. Plenum Press, New York.
Floyd, S. K. and Friedman, W. E. (2000). Evolution of endosperm developmental patterns among
basal flowering plants. Int. J. Plant Sci. 161 Suppl. S, S57-S81.
Simpson, Michael G. 2010. Plant Systematics. 2nd edition. Elsevier Academic press.
Stanley, R.G. and H.F. Linskens. 1974. Pollen biology, BiochemistryManagement. Springer–
Verlag, Berlin Heidelberg New York, p 67.
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DATA SHEET
Exercise No. 4
The Endosperm and the Seed
V. RESULTS AND OBSERVATIONS
A. Dry Bean Seed
B. Germinated Bean Seed
C. Dry Corn Seed
D. Germinated Corn Seed
E. Castor Bean Seed
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F. Mature Coconut Fruit/Seed
G. Fill out the table below.
Vigna radiata
Zea mays
Ricinus communis
Cocos nucifera
VI. CONCLUSION:
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plumule
radicle
hypocotyl
epicotyl
coleoptiles
scutellum
seed coat
tegmen
testa
Type of
endosperm
development
raphe
No. of
Cotyledo
ns
micropyle
Type of Seed
hilum
Mark ✓ if present, X if absent
VII. GUIDE QUESTIONS:
1. What is embryogeny and on what criteria are different embryogeny types based?
2. Name four seed storage tissue origin types. Of what three major chemicals are seed
storage tissues composed?
3. In what particular type of endosperm is haustorion formed? Explain.
4. What is the meaning of haustorium?
5. Name the three basic types of endosperm development and describe how they differ.
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reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other
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6. Other than endosperm, what two other seed storage tissue origins occur in angiosperms?
7. Give the origin of the following: scutellum, testa, tegment and endosperm.
8. Give the difference among the 4 types of seeds being studied.
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This document is a property of the Biology Department of Central Mindanao University. No part of this document may be
reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other
electronic or mechanical methods, without prior written permission of the publisher.