1. Seed Plants – Gymnosperms

2. Sub-Phylum Spermosida – Seed Plants
Class: Coniferae
Characteristics
gymnosperms (gymno = naked; sperm = seed)
Sporophyte larger than gametophyte
Most are trees or shrubs with woody tissue
Leaves are often needles or scales
Produces cones with two types of spores
Seeds usually produced on surface of scales of cones

3. Most ancient surviving seed plants. Three Classes:
Gymnosperm Evolution
Most ancient surviving seed plants. Three Classes:
Cycadae
Ginkgoae
Conifernae
Leaves evolved into specialized male and female reproductive structures called scales.
Scales are grouped into larger structures called male and female cones.
Male cones  gametophytes called pollen
Female cones  gametophytes called eggs
Once fertilization occurs the zygote grows into a seed that is held on the scales. The seeds are protected by a seed coat but the seed is not covered by the cone.
Because the seeds sit ‘naked’ on the scales, these plants are called naked seed plants  gymnosperms (gymno – naked; sperm – seed).

4. Gymnosperm Diversity - Cycadae
Cycads – palm-like plants but have naked seeds.
First appeared in the fossil record 225 million years ago - only 9 genera remain today
Habitat – Sub-tropical/tropical

5. Gymnosperm Diversity - Ginkgoes
Ginkgoes – common when dinosaurs rules but only one species remains today – Ginkgo biloba
Ginkgo biloba may be the only seed plant species alive today, thanks to Chinese gardeners

6. Gymnosperm Diversity - Conifers
Most bear seeds or cones
Needle-like or scale-like leaves with thick cuticles
Pines, spruce, firs, cedars, junipers, larches
Some live over 4000 years old and 1000 m tall

7. Old Trees
Methuselah, a 4,845-year-old Great Basin bristlecone pine (Pinus longaeva) in the White Mountains of California

8. Reproduction in Gymnosperms
FEMALE CONES
Called seed cones
House female gametophytes
Stays inside tissue of sporophyte (cone)
Produces ovules (plural = ovum)
Inside the ovule = an unfertilized egg
Very small
MALE CONES
Called pollen cones
Produce male gametophytes
Haploid spores: pollen grains
Inside pollen grains = 2 sperm (1N)
Very small

9. Alternation of Generations
In the spring, the male cone releases millions of dust like pollen grains that are carried on the wind to the female seed cone. (not all make it to the seed cone)
Once a pollen grain lands near a female gametophyte, it produces a pollen tube that grows into the female gametophyte until it reaches the egg.

10. Alternation of Generations
inside the pollen tube are 2 sperm (1N), one sperm fertilized the egg, the other disintegrates.
These sperm cells burst out of the pollen grain and fertilize the ovule (egg).

11. Alternation of Generations
After fertilization – the zygote grows into an embryo encased in what later becomes the seed. Embryo + stored food + coat = seed
Mature seeds drops out of cone onto the ground.

12. Alternation of Generations
Seed germinates and seedling grows into a mature plant.
When mature, the adult plant produces cones

13. Wood
Xylem tissue conducts water and dissolved materials (called sapwood)
Xylem forms outer rings of stem – “wood”
Growth rings
Xylem produced usually in late spring and early summer (thick at this time of year)
During fall and winter thin xylem is produced (therefore you can count the rings)

14. Wood
Heart wood: older, darker wood at the center of the tree trunk that is full of resins, gums and pigments.
May rot without affecting the functions of the tree.
Resin ducts – secrets resin which stops growth of fungus and invasion of insects.
When distilled, resin  turpentine

15. Wood
Rays
Radiating out from the center of xylem and phloem, they transport nutrition and water radially across cells

16. Wood
Cambium
Thin sheets of unspecialized cells between central xylem of stem and phloem of inner bark
Cells of Cambrian divide by mitosis
If near phloem  becomes phloem
If near xylem  become xylem
Cambium layer adds new cells that increase the width of the stem
As xylem expands it destroys phloem, therefore there is no increase in the thickness of phloem

17. Meristematic Tissue
Cells capable of dividing through out the life of the plant (= growing)
Only plant tissue that produces new cells through mitosis
As new cells mature they differentiate into many different kinds of tissue
Apical meristems allow the tips of stems and roots to grow in length
Cork cambium produces outer covering of stems
Vascular cambium produces vascular tissues (xylem and phloem) and increases the thickness of stems over time
Pericycle allows roots to grow thicker and branch out

18. Surface Tissue
Forms the outer or surface layer of leaves, stems and roots
Surface tissue in tree bark protects against water loss
Surface tissue in roots helps in the absorption of water