This division, commonly known as flowering plants or angiosperms, is characterized by the presence of reproductive organs called flowers, within which the spores (megaspores or microspores) are produced, and resulting eventually in the production of seeds enclosed in the protective fruit.  This is the largest and most diverse group we have studied.

I.  Floral Structure
 Depending upon Spring weather and availability, a number of different flowers will be collected and brought into the lab for dissection (alternatively, preserved flowers will be used).  These will be selected, insofar as possible, to demonstrate the major variations and types of flowers.  Dissect one flower of each type determining which of the various parts are present (receptacle, sepals, petals, hypanthium, stamens, pistils with ovary, style, stigma, etc.) and whether the flower is hypogynous, epigynous, or perigynous (see Fig. 21-6 et al).  Further information regarding the specific flowers will be provided in the laboratory.
 
 
 
 
 
 
 
 

II.  Floral Anatomy
 Study the prepared slides bearing longitudinal flower sections of the following species:

A.  Brassica oleracea (cabbage & its allies)
 This is a good example of a “typical” hypogynous flower.  Identify the receptacle, sepals, petals, stamens (filament, anther, & pollen) and pistil (ovary, ovules, style, and stigma.  Why do you suppose the cells of the anther walls have spiral thickenings on their walls?

B.  Ribes (currants & gooseberries)
 The flowers of this genus are epigynous.  Identify the receptacle, hypanthium sepals, petals, stamens (filaments, anthers, and pollen) and pistil (ovary, ovules, style and stigma).  Is the ovary superior or inferior?

C.  Malus (apple)
 The apple flower is another good example of an epigynous flower (Fig. 21-12).  Identify all parts as above.

D.  Prunus (cherries & plums)
 Members of this genus are excellent examples of perigynous flowers (Fig. 21-13).  Identify the hypanthium as well as all the parts listed for the above flowers.  Is the ovary superior or inferior?
 

E.  Lilium (lily)
 The slides you will study (below) for microsporogenesis-pollen formation and for megasporogenesis-embryo sac development also belong to this genus.  Study this longitudinal section of a young lily flower bud, identify all parts and compare carefully to the lily flower cross sections you will study below.  Is this flower hypo-, epi- or perigynous?
 

III.  Microsporogenesis and Pollen Formation
 Study the prepared slides dealing with pollen formation in this order: 1) Lilium: young anthers; 2) Lilium: anthers x.s. (first division); 3) Lilium: mature anthers x.s. (Compare to Fig. 21-14).
 Follow the sequence of development within the anthers from microsporocytes (slide #1, compare Fig. 21-14a) through first meiotic division (slide #2) to the mature pollen (slide #3), compare Fig. 21-14b).  Be sure you know the ploidy level (n or 2n) or of the various cells and tissues in each slide.  Note the changes that take place in the walls of the pollen sacs (=microsporangia) from one slide to the next.  What is the tapetum and what is its function?  The mature pollen (slide #3) has a readily visible tube nucleus.  With careful searching you may be able t find a pollen grain sectioned so that both the tube nucleus and the generative cell can be seen (see Fig. 21-16).  Notice the elaborate sculpturing that develops on the outer surface of the pollen grains.   Be sure to identify all other flower parts in these cross sections.
 

IV.  Megasporogenesis, Embryo Sac Development, and the Young Embryo
 Lilium-type embryo sac development is somewhat more complex than the more frequent Polygonum-type.  The life cycle diagram for soybean in your text (Fig. 21-23) illustrates the Polygonum-type.  However, since no other material is generally available for study, it is the Lilium-type that we will concentrate on in this lab.  Study each of the four prepared slides in sequence and by using lecture notes, etc., identify the place of each slide in the entire sequence.  Be sure you understand the changes in ploidy level, etc. that take place in this process (these slides are particularly expensive, so please be extra careful with these slides).

 Slide #1:  Lilium ovule, megasporocyte
 Slide #2:  Lilium ovule, megaspores [i.e., the 1st 4-nucleatte stage]
 Slide #3:  Lilium ovule, 2nd 4-nucleate stage
 Slide #4:  Lilium, early embryo

 Follow the sequence of events in these slides from the young ovule containing a single mature megasporocyte (slide #1; compare fig. 21-18a) nearly ready to undergo meiosis, resulting in the production of 4 megaspore nuclei (slide #2) which remain in one cell (now referred to as a young embryo sac).  These 4 nuclei migrate, one to the micropylar end where it divides by normal mitosis, and the other three to the opposite end where they divide on a shared spindle.  These divisions result in the 2nd 4-nucleate stage (slide #3) with 2 haploid and 2 triploid nuclei in the embryo sac.  Each of these four nuclei divides one more time (normal mitosis) to form an 8-nucleate embryo sac (see Fig. 21-18c).  Following nuclear migration and double fertilization (Fig. 21-20), free-nuclear endosperm and a young embryo begin to develop within the embryo sac (slide #4).
 
 

Be sure to note the other changes that take place in the maturing ovules while this sequence of events is occurring within the embryo sac.

 What is the function of the integuments?
 What is the ploidy level of the megasporocyte?
 What is the ploidy level of the various embryo sac nuclei?
 What is the ploidy level of the integuments?
 What is the ploidy level of the other ovary tissues?
 What is the ploidy level of the embryo?
 

V.  Embryogeny in Flowering Plants
 The development of the flowering plant embryo is best studied in Capsella bursa-pastoris, a common weed belonging to the mustard family (if available, it may be one of the flower types brought into lab for you to dissect in part 1 above).  Although embryogeny in flowering plants is not as complex as it is in animals, it does nevertheless present a very ordered and predictable set of occurrences which take some effort to understand and appreciate [be sure to read the narrative and look at the figures (photomicrographs) in the text explaining the process, pp. 557-559-].
 We have a series of 4 slides for you to study, which show sequential stages in Capsella embryo development.  Study the 4 slides in sequence, carefully observing the structures as pointed out below.  These slides actually bear sections through nearly entire Capsella fruits with a number of seed visible in each.  Probably only one or two of these seeds will exhibit a good sectional view (i.e., more or less median) of the embryo inside, and this is the one you should seek and study, according to the notes below (but some of the others may show different sectional views which cast light on the subject as well).  The following notes emphasize the growth and changes in the embryo itself, but as you examine the slides be sure to observe and understand the concurrent changes that take place in the rest of the seed, especially the endosperm and the seed coat.  [Note: the seeds (and also the contained embryo sacs) of Capsella are bent almost 180°, so that the micropyle and the funiculus are next to one another rather than at opposite ends of the seed as usually shown in diagrammatic representations of ovule development.]
 

Slide 1 – CAPSELLA: embryo before cotyledons
 These slides show a stage comparable to Fig. 23-3e (or perhaps between Fig. 23-3c & 20-3d), where the cotyledons are just starting to form.  On the embryo, identify the suspensor with large sac-like basal cell, the embryo with root tip and (very young) cotyledons.  Also identify and examine the seed coat, the endosperm and the antipodal tissue.
 

Slide 2 – CAPSELLA: early cotyledons
 The embryos on this slide are somewhat larger and the cotyledons are better developed, but are not or only barely beginning to bend (similar but not quite to the stage shown in Fig. 23-3e).  Identify all the same parts and structures mentioned for slide 1.

 
Slide 3 – CAPSELLA: embryo, bending cotyledons
 This slide shows an embryo stage similar to or just beyond that shown in Fig. 23-3e.  They are not quite median sections and so the suspensor is not visible or at least does not appear complete and attached.  Identify all the same parts as above.
 

Slide 4 – CAPSELLA: embryo mature
 Compare these embryo sections (many visible) to Fig. 23-3f being sure to identify the cotyledons, shoot apical meristem (epicotyl), and hypocotyls-root axis.  Can you distinguish the procambium?  What has happened to the endosperm at this stage compared to the previous three slides?  How has the nature of the seed coat changed in these nearly mature seeds compared to the younger ones above?

IV.  Fruits and Fruit Classification
 During the time that the seeds and the embryos inside them are maturing, the ovary or ovaries (sometimes with other floral tissues) develops into a specialized seed-container called a fruit. Fruits are very diverse in form and function, but can be classified into types based upon characters such as: texture, presence or absence of a mechanism for dihiscence (opening), number of pistils (and/or flowers) involved in forming a single fruit, whether or not there are other flower tissues (in addition to the ovary) involved in fruit development.  Use pages 543-548 in your text for background information.

 Examine the small variety of different fruit types available in lab and, using the outline-key presented below, identify them.  As you examine each fruit type, ask yourself these questions:
 -How can you tell how many individual flowers or pistils comprise a fruit?
 -How can you tell if it developed from a simple or compound pistil?
 -How can you tell if it developed from a superior or inferior ovary?
 -Is the fruit dehiscent or indehiscent?
-What role do various fruits have in addition to protecting seeds during development?
 

A Simplified Outline of Common Fruit Types

I.  SIMPLE FRUITS – the product of a single pistil

  A.  Fleshy Fruits
 
 1) Texture homogenous,   fleshy throughout
  BERRY – derived from a superior ovary
  (tomato, pepper, grape, avocado, eggplant, persimmon)

  FALSE BERRY – derived from an inferior ovary
  (cranberry, gooseberry, currant, blueberry, elderberry, honeysuckle)

 
 
2) Texture heterogeneous
a)  Exterior firm, with a hard or leathery rind

HESPERIDIUM – derived from a superior ovary, distinctly segmented in cross section
(orange, lemon, and other citrus fruits)

 PEPO – derived from an inferior ovary, not distinctly segmented
 (melon, squashes, cucumbers, banana)

b) Exterior soft, with a hard or cartilaginous inner layer

DRUPE – derived from a superior ovary; fleshy part consisting of mesocarp, the endocarp forming a hard central ‘pit’ or stone around the seed
(peach, plum, cherry, almond, walnut, olive, coconut)

POME- derived from an inferior ovary; fleshy part derived form mesocarp and also from the hypathium, the endocarp thin and cartilaginous around the many seeds
(apple, pear, etc.)

B. Dry Fruits

1) Dehiscent, opening when ripe to release seeds

 a) Developed from a simple pistil (1 carpel)
 
 LEGUME – Dehiscing by two longitudinal sutures
 (beans, peas, peanuts, most Leguminosae)

 FOLLICLE – dehiscing along a single longitudinal suture only
 (milkweed, dogbane, Delphinium, peonies)

c) Developed from a compound pistil (2 or more carpels)

CAPSULE – developed from various types of superior or inferior ovaries; the following subtypes, based on type of dehiscence, are often recognized:
SEPTICIDAL CAPSULE – sutures forming at the septa; usually more than 2 carpel
(Yucca)

LOCULICIDAL CAPSULE – sutures forming in the locules; usually more than 2 carpels
(Iris, tulip)

PORICIDAL CAPSULE – dehiscing by small pores near the top; usually more than 2 carpels
(poppy)

CIRCUMSCISSILE CAPSULE – dehiscing by a lid
(Amaranthus; 1-seeded Utricle)
(plantain, Portulaca; several-seeded Pyxis)

SILIQUE – elongate, narrow capsule, composed of two carpels, the pericarp falling off as two valves, leaving the persistent septum which bears the seeds on its margins
(various mustards [Cruciferae])

SILICLE – similar to a silique, but short, not much longer than wide
(Shepherds Purse and other Cruciferae)

2.    Indehiscent, lacking special methods for opening; usually one or two seeded

 SAMARA – fruit winged for wind dissemination
 (elm, ash, tree-of –heaven, hoptree)
 
SCHIZOCARP – carpels two to many, united when immature, splitting apart at maturity
(but the seeds remaining within)
(Umbelliferae, Malvaceae, Labiatae, maples)

NUT – developed from a compound pistil (but only one carpel and one seed developing); the pericarp hard and stoney
(acorn, chestnut, hickory nut, hazelnut)

CARYOPSIS (Grain) - developed from a simple pistil, pericarp fused to the seed (corn, wheat, rice and other grasses)

ACHENE – developed from a simple-pistil, with superior ovary, pericarp not fused to the seed
(buckwheat, sedges, Ranunculus)

CYPSELA – developed from a simple pistil with inferior ovary, pericarp not fused to the seed
(sunflower, dandelion, & other composites)

II.  COMPOUND FRUITS – the product of two or more pistils

 AGGREGATE FRUITS – derived from several pistils of a single flower.
 (strawberry, raspberry, blackberry)

MULTIPLE FRUITS – derived from several to many flowers in an inflorescence
 (pineapple, mulberry, fig)

III.  ACCESSORY FRUITS
 Many of the fruit types described above sometimes incorporate hypanthium, receptacle or other non-pericarp material into the fruit.  These are referred to as accessory fruits
(fig, pineapple, strawberry, blackberry)