LAB 3

FLOWERS

• flowers are the defining features of the angiosperms
• flowers are NOT organs - there are only THREE organs in plants (root, stem, leaf)
  
• flowers are considered to be a modified branch system

General Terminology

• Perfect Flower - a flower with both male and female reproductive parts
• Imperfect Flower - a flower with either male or female reproductive parts
• Staminate Flower - a male flower
• Carpellate Flower - a female flower
• Monoecious - plants which have male and female flowers on a single individual (bisexual plants, both male and female on the same plant)
  
• Dioecious - plants which have male and female flowers on separate individuals (male and female plants)

MORPHOLOGY

• Review the lab manual to be able you can name and identify the functions of all floral parts
  

This diagrams the basic morphology of a typical flower.
Not all flowers have parts like this - often parts are reduced, highly specialized or even absent.
Also, the number of floral parts varies greatly.


This is a top view of Hypericum. Note the numerous stamens.
Is this flower actinomorphic or zygomorphic?


This is a cross section through Hypericum. Is this flower perfect or imperfect? Do the terms staminate and/or carpellate apply to this flower?
NOTE: I spelled Receptacle incorrectly in the diagram.


This is a cross-section through the ovary of Hypericum.
Can you distinguish the 5 carpels?
The ovules are in axile placentation - what are other types of placentation you know of?



POSITION OF OVARY

• There are 2 ways in which an ovary can be positioned.
  
• It can either be above the stamens, petals and sepals (superior)
• It can be below these three parts (inferior).

A superior ovary.


An inferior ovary.


A superior ovary can be within a hypanthium. Because a hypanthium is a fusion of sepals, petals and stamens and originates under the ovary, even though it looks like an inferior ovary, it is indeed superior.
Thank you to David Webb of the University of Haiwaii for this diagram.



COMPOSITE FLOWERS

• Often flowers are arranged in an inflorescence
• An inflorescence is simply the manner of arrangement of flowers on a particular plant
• In the composite flowers, Asteraceae, the flowers are arranged in a radial head.

NOTE: because this family will be covered in LAB 6, there will be only basic information here.


This picture shows the two types of flowers (or florets) found in a composite head.
The disk flowers contain the male and female reproductive organs (perfect).
The ray flowers contain the showy petals and only female reproductive organs (carpellate).


Cross-section through a sunflower. Compare this to the diagram on page 33 of the lab manual.


Compare this picture to the diagram of the disk flower on page 33 of the lab manual.
Keep in mind how much variation is possible and that diagrams never perfectly match all species within a particular family. The lab exam will most definitely contain LIVE material, it is important to be able to understand a diagram and then apply it to live specimens.


MONOCOTS VERSUS EUDICOTS

• Monocots generally have flower parts in multiples of 3's
• Eudicots generally have flower parts in multiples of 4's or 5's

In lab we were asked to distinguish between cross sections of a eudicot and a monocot flower.
The explanation on how to do this is diagrammed below.



Click to enlarge.

These are the raw slides, as they would appear under a microscope.


Click to enlarge.

This is a simple way of going about this:

The right slide is likely the monocot because of the the three distinct carpels visible in the middle.

The left side only has two carpels, and thus since this is neither a multiple of 3, 4 or 5 -> we can't use that quick rule to distinguish it. However, instead of using carpels, I have highlighted the sepals, of which there are 4. You can do the same for the petals. Because there are 4 sepals, this is likely the eudicot.






POP QUIZ


Can you describe the ovary positions in these three flowers?