Seeds and Fruits

In a previous exercise, you observed the flower and its many parts. You were also introduced to the events leading up to the fertilization of the egg by the sperm. The resulting cell was called the zygote. This develops into the embryonic plant. Plants also produce a second sperm cell that fuses with the polar nuclei to form a triploid endosperm. The endosperm accumulates much storage material that is used for the development of the embryonic plant. The embryo and the endosperm reside in the ovule and together these constitute a SEED. Of course the seed is contained within the ovary of the carpel; the gynoecium will develop to form a FRUIT surrounding the seeds. Today you will study the seed and fruit of the flowering plants

I. Seed Formation

The ENDOSPERM starts developing immediately after double fertilization, forming a parenchymatous tissue between the nucellus tissues of the ovule and the young embryo. The endosperm divides actively during early development of the seed; later it may store considerable amounts of food material, or it may transfer the food materials to the cotyledon(s) of the embryo and disappear completely. Meanwhile, the zygote undergoes a regular sequence of divisions to form an EMBRYO organized into a central hypocotyl with ROOT APEX (radicle) at one end and one or two COTYLEDONS and small SHOOT APEX at the other. The integument(s) of the ovule become(s) modified to form the SEED COAT. The entire structure--seed coat, endosperm if still present, and embryo--constitutes the SEED and is shed from the parent plant at maturity. The seed usually can withstand quite adverse conditions and remain dormant for considerable periods of time. It serves to disseminate the species.

Observe the demonstration slides of young seeds in Lilium and/or Capsella showing developing endosperm and a young embryo.

In the remaining space, diagram and label a seed of Capsella. Be sure to use the labels printed in bold above!


II. Fruit

The angiosperm seed is derived from the ovule which occurs within the ovary of the carpel. Changes in the ovary wall occur simultaneously with the maturation of the seed, giving rise to a FRUIT. Fruits are of various types--fleshy or dry and, when dry, dehiscent or indehiscent. In some species it may be the fruit with its contained seed(s) which is shed and distributed rather than the seed itself.

A classification of some common fruit types is given below. Use this to classify the several different fruit types available in the laboratory. Note that a number of common foods are included and that many of these are erroneously classified as "vegetables" when they are actually fruits!

THREE FRUIT CLASSIFICATION SCHEMES

  1. ORIGINS
    1. Simple fruit - formed from a single pistil (lily, apple, cucumber)
    2. Aggregate fruit - formed from a cluster of separate pistils borne in a single flower (raspberry)
    3. Multiple fruit - formed from the pistils of several to many flowers consolidated with other floral or inflorescence parts (pineapple, fig)
  2. COMPOSITION
    1. True fruit - composed of only the ripened ovary, with its contained seeds (lily)
    2. Accessory fruit - composed of the ripened ovary with other additional parts, such as receptacle, bracts, portions of perianth, etc. (apple, cucumber, fig)
  3. DESCRIPTIONS
    1. Fleshy Fruits
      1. Berry - few to many seeded, fruit coat soft and fleshy throughout (grape, banana)
        1. Hesperidium - berry with tough rind (orange, grapefruit)
        2. Pepo - thick-skinned berry, accessory (squash, cucumber)
      2. Drupe - usually 1-seeded, fruit coat with fleshy outer and inner stony layers (peach, plum, olive, raspberry, almond)
      3. Pome - fleshy accessory fruit with cartilaginous core (apple, pear)
    2. Dry Fruits
      1. Indehiscent Fruits
        1. Achene - 1-seeded, fruit coat free from seed coat (buttercup, sunflower)
        2. Caryopsis (grain) - 1-seeded, fruit coat fused with seed coat (corn, wheat)
        3. Samara - 1-seeded, fruit with winglike outgrowth (ash)
        4. Nut - 1-seeded, thick hard wall, partially or completely surrounded by cup or husk (oak, hickory, walnut)
      2. Dehiscent fruits
        1. Follicle - single carpel splitting along one side only (milkweed, magnolia)
        2. Legume - single carpel splitting along both sides (bean)
        3. Capsule - compound pistil, splitting lengthwise or by pores (lily, iris, poppy)

Examples:

Raspberry:aggregatetruedrupe
Apple:simpleaccessorypome
Mulberry:multipletruedrupe


A. The Peanut

Examine the peanut provided very carefully and dissect it as needed to answer the following:
Which flower parts are still visible?stigma
sepal     petal     stamen     style
ovary
How many pistils were there in the gynoecium? 
How many carpels were there in the gynoecium? 
Is the pistil simple or compound?simple       compound
What is the redskin? 
How many large fleshy structures are inside the redskin? 
What are these fleshy structures called? 
To what class of the flowering plants does the peanut belong? 
What is the purpose of the fleshy structures? 
What chemicals do they naturally contain (taste!)? 
Do you find a miniature plant inside these fleshy structures?yes       no
What part of a seed is conspicuous by its absence? 
Classify the peanut fruit in terms of origin: 
Classify the peanut fruit in terms of composition: 
Classify the peanut fruit in terms of description: 
When we eat peanuts without the redskin, do we eat a fruit, a seed, or what? 
When we eat peanuts with the redskin, what are we eating? 
Some people eat the peanuts in the "husk" or "shell" (need more fiber in your diet?)! What are these people eating? 


B. The Snow Pea Fruit

Examine the snow pea fruit very carefully and dissect it as needed to answer the following:
Which flower parts are still visible?stigma
sepal     petal     stamen     style
ovary
How many sepals were in the flower? 
Is the style and stigma present?yes       no
Was the ovary superior or inferior?superior       inferior
The flower was:hypogynous   perigynous   epigynous
The pea has a dark stripe running along one side,
but lacks this stripe on the other side.
Which side has the placenta?
The side with the stripe
The side without the stripe
How many locules were there in the ovary? 
How many pistils were there in the gynoecium? 
How many carpels were there in the gynoecium? 
Is the pistil simple or compound?simple       compound
How many ovules are in the locule? 
What color is the ovule? 
Do you think that the ovules have become fully mature seeds?yes       no
Classify the pea fruit in terms of origin: 
Classify the pea fruit in terms of composition: 
Classify the pea fruit in terms of description: 


C. The Cherry Tomato Fruit

Examine the cherry tomato fruit provided very carefully and dissect it as needed to answer the following:

Which flower parts are still visible?stigma
sepal     petal     stamen     style
ovary
How many sepals were in the flower? 
Is the style and stigma present?yes       no
If not, to which end of the fruit was it attached? 
Was the ovary superior or inferior?superior       inferior
The flower was:hypogynous       perigynous       epigynous
How many pistils were there in the gynoecium? 
How many locules were there in the ovary? 
How many carpels were there in the gynoecium? 
Is the pistil simple or compound?simple       compound
The tomato has solid walls and a solid center
with seeds in between. Is the placenta attached
to the walls or to the center of the fruit?
walls       center of fruit
How many ovules are in each locule?one       a few       many
What color is the ovule? 
Classify the tomato fruit in terms of origin: 
Classify the tomato fruit in terms of composition: 
Classify the tomato fruit in terms of description: 


D. The Strawberry Fruit

Examine the strawberry fruit provided very carefully and dissect it as needed to answer the following:
Which flower parts are still visible?stigma
sepal     petal     stamen     style
ovary
How many sepals were in the flower? 
How many pistils were there in the gynoecium? 
How many carpels were there in the gynoecium? 
Is the pistil simple or compound?simple       compound
Is the style and stigma present?yes       no
Was the ovary superior or inferior?superior       inferior
The flower was:hypogynous       perigynous       epigynous
From what part of the flower is all the red tissue? 
What color is the true strawberry fruit? 
Classify the strawberry fruit in terms of origin: 
Classify the strawberry red tissue in terms of composition: 
Classify the strawberry true fruit in terms of description: 


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