INTRODUCTION:

 The goal of this laboratory is to turn your senses and intellect on to the phenomenal structures commonly known as fruits.  In flowers we observed that the ovary, style, and stigma compose the pistil, and that the ovary is a protective vessel in which ovules are nourished to their mature form--seeds.  We learned that the ovary, with time, evolved through the constant modification of leaf material.  This modification of leaf material provides protection and facilitates dispersal of the seeds.  Protection came about by the initial infolding of the leaf to form an enclosed vessel.  Within this ovarian vessel, the ovules remain attached to parent tissue along zones of placentation.  We refer to these zones of placentation as carpels.  Ovaries can be composed of one to numerous 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.
 
 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; mammals to fish.  Modifications in the shape, structure, and often color of the protective 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?

 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.  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 phenomena!

I. Angiosperm gynoecia essential for human survival:
 

1. LEGUME: Single carpel, multi-seeded, dehiscent along two sutures (wild types), seed mostly young 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 starch), 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.
 

3. 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]
 

4. 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]

5. 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

6. 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

7. HESPERIDIUM: a 'special' berry with numerous carpels (separable as 'sections'); locules filled by plump cells;pericarp covered by oil glands. Fruit produced by the genus Citrus.
 

• Orange, lemon, lime, grapefruit - distinctive essential oils
 

8. POME: a 'false fruit' that is formed by fusion of the HYPANTHIUM [flower epigynous] to the ovary, with the hypanthium forming the edible portion.
 

• Apple/Pear - note sepals opposed to the pedicel [epigyny], internal demarcation between ovary wall and hypanthium, locules of ovary

9. 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 the central RACHIS of both pineapple and maize ear (cob) - hard, fibrous = vascularized shoot (as opposed to peri
• carp) tissue.
• Fig - inflorescence enclosed within receptacle tissue (syconium)

10. NUT : a dry, indehiscent, 1-seeded fruit with a hard exocarp
 

• Pecan - edible portion is embryo and cotyledons

11. CAPSULE : a dry, dehiscent fruit made up of several carpels.  The ripe pericarp splits open along pores or slits.
 

• Okra - capsule eaten while green

 Carefully examine the fruit material provided.  On a separate piece of paper, list the fruits on display, paying special attention to their morphology, structure, family and scientific name, and geographic origin.  During the exercise, answer the following questions for each fruit observed.
 1.  What is the fruit type?
 2.  How many carpels are present?
 3.  Think about the different fruit types and how they might be dispersed in nature.
 
 
 
 
 
 

QUESTIONS FOR THOUGHT, REVIEW, AND STUDY

1.  What are two ways to count the number of carpels in a fruit?
 
2.  Draw simple diagrams of various placentation types.

3.  Draw a cross-section of a fruit which has 3 carpels, 1 locule, and parietal placentation.

4.  Draw a cross-section of a fruit which has 3 carpels, 3 locules, and axile placentation.

5.  Follicles and capsules are similar in that they both contain numerous seeds.  How do these two fruit types differ?

6.  What is meant by the word epigynous?  So, do epigynous flowers have inferior or superior ovaries?

7.  What is a berry?  List some examples.

8.  What is a hesperidium?  List some examples.

9.  What is a pepo?  How many carpels do pepos typically consist of?  What family is characterized by the pepo?

10.  Berries are usually sweet and many-seeded.  Do you think these fruits are dispersed by wind or animals?

11.  What is a samara?  Give an example.  How is it dispersed?

12.  What is an aggregate fruit?  List some examples.

13.  What is a multiple fruit?  List some examples.

14.  What is an accessory fruit?  A strawberry is an example of an accessory fruit.  What are we eating when we eat a strawberry?

15.  What are we eating when we eat an apple?  What type of fruit is an apple?  How about a pear?

16.  What is a drupe?  Draw a cross-section of a drupe and label the parts.  List some examples of fruits which are drupes.  Why are drupes often referred to as stone fruits?

17.  The legume fruit type characterizes the bean family.  Describe or define a legume; i.e., how many carpels are they composed of and how do they dehisce?

18.  What is an achene?  List some examples.

19.  Why might apples be bright red and sweet in nature?  Also, why might the native apples be much smaller than the apples now cultivated by human beings?

20.  What is your favorite fruit?  What is the fruit type?

21.  How many carpels are present in a cucumber?  What is the fruit type?

22.  What is an apricot?

23.  What is an artichoke?  In what family is it included?  What are we eating when we eat an artichoke?

24.  Okra is in the cotton family, the Malvaceae.  What type of fruit is okra?  It has many seeds and is comprised of  more than one carpel.  On that note, does okra originate from a simple or compound pistil?  Is okra ripe when we eat it (are the seeds ready to be released)?

Last Updated 7/12/98