PLANTS AND PEOPLE - FRUIT LAB
This lab is ready
for
print-out. Note that it is in THREE PARTS (next two linked at
bottom)--you will need all of them. For best results, DON'T print
from this page and the ones linked from the bottom. Instead, click this link for a PDF that will print
everything properly. There may be a few fruits to add in lab--we never
know what the local stores are going to have.
You can download Ratna's
powerpoint here.
INTRODUCTION:
The goal of this laboratory is to
introduce you to the wonderful world of fruits. In the flower
lab, we observed that the ovary, style, and stigma make up the pistil,
and that the ovary is a protective vessel in which ovules are nourished
to their mature form--seeds. Recall that the closed carpel
evolved via infolding of the leaf to form an enclosed
vessel. Each of these vessel units is a carpel with its own
line of placentation or zone of ovule/seed attachment. The
fruit provides protection and facilitates dispersal of the seeds.
Ovaries and fruits can be composed of one to many free or fused
carpels. The number of ovules associated with each carpel, and
thus the number associated with the ovary, can vary from one to
many. Also, ovaries can be separated into several distinct
chambers or consist of only one chamber. These chambers are
called locules. The number of locules is often (but not always)
equal to the number of carpels. Remember to check the number of
placentae, too.
Dispersal of seeds in nature is accomplished
in many ways. Seeds can be dispersed by animals, wind, water,
etc. Animal dispersers range from insects to birds to mammals to
fish. Modifications in the shape, structure, and often color of
the ovary directly correspond to the ways in which seeds are
dispersed. Bright red, fleshy berries are commonly dispersed by
fruit-eating birds. Winged fruits, such as those found on maple
trees, have obviously come about through modifications which facilitate
wind dispersal. How might nuts, such as acorns, be
dispersed? What animals have you observed eating and burying
acorns in the autumn? What characters would a water-dispersed
fruit have?
By the end of this laboratory
exercise you should be able to recognize the various fruit types which
are present in nature and understand the similarities and differences
between these fruit types. You should become familiar with the
terminology used to describe fruits, such as carpel, ovule, zones of
placentation, etc. You should be able to count the number of
carpels present in a given fruit and to recognize the arrangement of
these carpels within the ovary—the placentation
type. Lastly, and most importantly, you should be able to
recognize by name (common, scientific, and/or family name) the fruits
displayed. You should leave the laboratory with a deeper
appreciation for the fruits of the flowering plant world and-- a
stomach full of these incredibly delicious props!
I. Fruits essential for human survival:
1. LEGUME: Single carpel, multi-seeded,
dehiscent
along two sutures (wild types), seed consists mostly of young embryo
sporophyte (high protein):
- Peanut - geocarpic, pericarp, testa,
cotyledons
(high protein
- endosperm converted to embryo - true of most FABACEAE [Leguminosae].
- Green Bean - single line of ovules (nearly
mature)
- Snow Pea - ovules and fruit, less mature
2. CARYOPSIS: More than one carpel BUT only a
single
seed. Seed, mostly endosperm (high in starchstarch) The seedcoat
is fused to the pericarp
- Corn (maize) -
FRUIT
is a CARYOPSIS but the EAR is a MULTIPLE
fruit [fruits from separate flowers of a single INFLORESCENCE combined
in a single structure. Note inflorescence stalk [RACHIS] or corncob.
- Other true grains--rice, wheat, oats, rye,
barley, sorghum.
II. Other fruits and fruit-like structures:
3. ACHENE: More than one carpel, one seed,
pericarp
a single layer of tissue and SEPARATED from the seed. The CARYOPSIS
[fruit
of the grass family - POACEAE] is similar in structure BUT pericarp and
seed are united.
- Sunflower - Fruit [for the birds] and seed
[for
people]
- Strawberry - FRUIT is a tiny achene (many
positioned in 'pits'
that occur in the expanded, red, sweet RECEPTACLE of the 'AGGREGATE
FRUIT'
[a 'false' fruit]
4. NUT : a dry, indehiscent, 1-seeded
fruit
with
a hard exocarp. The ovaries that produce nuts have
more than one carpel, but through abortion, only one seed matures.
- Pecan - edible portion is embryo and
cotyledons
5. CAPSULE : a dry, dehiscent fruit made
up
of several
carpels. The ripe pericarp splits open along pores or slits.
- Okra - capsule eaten while green
6. DRUPE: Single carpel, single-seeded,
pericarp
tissue differentiated into THREE layers: EXOCARP, MESOCARP, ENDOCARP:
- Peach - exocarp with fuzz
- Nectarine, plum, and cherry - exocarp
without
fuzz
- Almond - exocarp/mesocarp removed, just
PYRENE
[=endocarp
and seed]
- Avocado - endocarp VERY thin
- Coconut - mesocarp fibrous ,[dispersal],
testa
thin, endosperm
both solid [meat] and liquid [milk]
- Raspberry - an AGGREGATE (separate ovaries
of one
flower
joined together) of small drupes [druplets]
7. BERRY: More than one
carpel, fleshy
[animal dispersed]
and many-seeded.
- Tomato (Roma and 'cherry') - two
carpels/locules
- primitive
- Tomato (normal) - extra septa and locules
- Peppers - midway between a CAPSULE [dry,
dehiscent] and a
berry
- Eggplant - selected for extra tissue - no
locules
- Kiwi fruit - leathery, fuzzy pericarp with
many
carpels,
seeds attached on a central mass of white tissue
- Banana - epigynous - 'peel' is a
combination
of
pericarp
and HYPANTHIUM - a sterile polyploid, ovules are aborted
- Blueberry - epigynous
- Grapes - clustered in panicles
8. PEPO: a 'special' BERRY from an
epigynous
flower
of the CUCURBITACEAE - leathery or hard 'rind' (Pericarp + hypanthium),
1 locule, and 3 lines of ovules.
- Cucurbita -
summer' squash vs.
'winter'
squash [pumpkin]
- Cucumber - entire fruit is consumed
- Watermelon - 90% water
- Honeydew, cantaloupe, musk melons - all one
species
9. HESPERIDIUM: a special type of berry
with
numerous carpels
(separable as 'sections'); locules filled by plump cells (which are
modified hairs!); pericarp with oil glands. Fruit produced by the genus
Citrus.
- Orange, lemon, lime, grapefruit -
distinctive
essential oils
10. POME: a 'false
fruit' that is formed by
fusion
of the HYPANTHIUM (of an epigynous flower) to the ovary, with the
hypanthium
forming the edible portion.
- Apple/Pear - note sepals on the opposite side
from the
pedicel (the flower is epigynynous) and
internal demarcation between ovary wall and hypanthium.
11. AGGREGATE FRUIT:
a multiparted fruit that develops from separate, simple pistils from
ONE flower.
- Blackberry/Raspberry--these are aggregations of
tiny drupelets.
12. MULTIPLE FRUIT: a fruiting
inflorescence
with
true fruits from separate flowers combined into a single unit
(essentially
a fruit-like infructescence). The maize ear is a unit formed
from
a pistillate inflorescence.
- Pineapple
- each perfect flower forms a
berry,
but they are
compressed together to form the pineapple. Note that the central RACHIS
of
both
pineapple and maize ear (cob) is a hard, fibrous, vascularized shoot
(as opposed to pericarp) tissue.
- Fig - inflorescence enclosed within
receptacle
tissue--this special fruit type is called a syconium
13. ACCESSORY FRUIT: a fruit in which the edible part is
derived from something other than the ovary.
- Strawberry--the real fruits are the little achenes (which
most people call seeds) and the juicy red part we eat is an enlarged
receptacle
- Apple--Apples may be placed in this category, since the
edible part is the hypanthium, not the ovary.
Go on to the Activity
Section, Fruit
Review Questions, Return to BOTN
328 homepage or
prior
lab session (flowers)
last updated 7/20/2007