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FRUITS• A “fruit” is derived from the ripened
ovary (ovaries) and sometimes other associated floral parts– to end the debate then, a tomato is a fruit
since it is derived from a flower• The fruit (usually a ripened ovary) is
surrounded by the fruit wall or pericarp– This wall is composed of three layers
(exocarp, mesocarp, and endocarp)– These layers may be distinct or fused
Fruit Types
• Multiple Fruits– derived from
MANY flowers– pineapple,
mulberry
For an interactive key to FRUIT TYPES, go to http://arnica.csustan.edu/key/key2.html
Fruit Types (cont.)
• Aggregate Fruits– derived from
SEVERAL separate carpels (pistils) of ONE flower
– strawberry, raspberry, blackberry
Fruit Types (cont.)
• Simple Fruits– derived from ONE carpel or pistil of ONE flower– are either fleshy or dry at maturity
Simple Fruits
• Fleshy Fruits (a few types)– with a fleshy hypanthium and/or receptacle =
pome (apple)– a single seed with stony endocarp = drupe
(plum, peach)– many seeded, endocarp fleshy = berry
(grape, tomato) or pepo (pumpkin, watermelon)
– Outer layer with a separable rind = hesperidium (orange, lemon, grapefruit)
Simple Fruits (cont.)
• DRY FRUITS– Dehiscent Types
• seeds released through one seam = FOLLICLE• seeds released through 2 seams = LEGUME• seeds released though pores or multiple seams =
CAPSULE
– Indehiscent Types• pericarp hard and thick with a basal cup = NUT• Pericarp soft and thin, no cup = ACHENE,
CARYOPSIS etc...
Why the variation in fruit types?
• Fruits are units of dispersal for the seeds
• Certain fruits are adapted for dispersal by wind (small, light, winged)
Fruit Dispersal (cont.)
• Others are dispersed by animals (fleshy, colored, sweet, or high in energy like nuts; or with spines, hooks)
Bidens – tickseed fuits
Seeds
• A seed is surrounded by the seed coat derived from the integuments
• The embryo may have large cotyledons (as in lima beans) and little endosperm
• Some seeds have lots of endosperm and thin cotyledons (castor beans)
The Grass Seed (Fruit)
• Outer pericarp is fused to the seed coat• Single massive cotyledon is called the
scutellum• Protective sheaths cover the early shoot
(coleoptile) and the root (coleorhiza)• Endosperm is surrounded by a special
layer of cells called the aleurone layer
Seed Germination
• Normal germination requires proper temperature, water, oxygen and sometimes light
• If, given proper conditions, a seed does not germinate, we say it is DORMANT
• Dormancy is annoying to us, but it is evolutionarily adaptive for the plant
Reasons for Seed Dormancy• Seed coat impervious to water and/or
oxygen (imbibition of water is often the first step in germination)– scarification required (physical or
chemical) to allow entry of water and/or oxygen
– many commercial applications for seed production
SeedDormancy
• Seed has an immature embryo
• Seed has chemical inhibitors in the seed coat that must be leached out
Seed Longevity
• Seeds may be dormant for only a few weeks to thousands of years– record is over
10,000 years for Arctic lupine seeds from lemming burrows
Seed Banks• Seed Banks help protect angiosperm
genetic diversity around the world
Kew Gardens, England. Home of the Millennium Seed Bank Project
Embryology
• Early embryo development in plants progresses through specific stages:
– much of the work done on Capsella bursa-pastoris (“shepherd’s purse”)
CapsellaEmbryology
(cont.)
– “heart-shaped” stage where the embryo’s two cotyledons become obvious and the differentiation of tissues become evident
CapsellaEmbryology
(cont.)
• “bending cotyledons” stage where the embryo moves toward its final form
Embryonic Tissue Layers
• Thee distinct tissue layers differentiate early in embryo development:– PROTODERM which will give rise to the
plant’s epidermis and all associate structures (guard cells, trichomes, epidermal cells)
– PROCAMBIUM which will become the primary xylem and phloem tissues (vascular tissues)
Embryonic Tissue Layers (cont.)
– GROUND MERISTEM from which will be derived the pith, cortex, and associated structures in the stem and root
• These tissue layers correspond in a way to early tissues in animal embryos, namely, the ectoderm, endoderm, and mesoderm
• Development of most plant embryos has not been investigated