Page 124 - Ultimate Visual Dictionary (DK)

PLANTS

Gymnosperms 1 LIFE-CYCLE OF SCOTS PINE
(Pinus sylvestris)

Needle
THE GYMNOSPERMS ARE FOUR RELATED PHYLA of seed-producing (foliage
plants; their seeds, however, lack the protective, outer covering leaf)
that surrounds the seeds of flowering plants. Typically,
Cone Ovuliferous scale
gymnosperms are woody, perennial shrubs or trees, with stems, (ovule- then seed-
leaves, and roots, and a well-developed vascular (transportat) system. bearing structure)
The reproductive structures in most gymnosperms are cones: male MALE CONES YOUNG FEMALE CONE
cones produce microspores in which male gametes (sex cells) develop; Pollen grain in micropyle Ovuliferous
female cones produce megaspores in which female gametes develop. (entrance to ovule) scale
Microspores are blown by the wind to female cones, male and female Pollen
gametes fuse during fertilization, and a seed develops. The four grain Ovule
(contains
gymnosperm phyla are the conifers (phylum Coniferophyta), mostly
Nucleus female
tall trees; cycads (phylum Cycadophyta), small palmlike Air sac gamete)
trees; the ginkgo or maidenhair tree POLLINATION
SCALE AND SEEDS
(phylum Ginkgophyta), a tall tree with
Pine Integument
bilobed leaves; and gnetophytes (Pinus sp.) (outer part Archegonium
(phylum Gnetophyta), a diverse Ovuliferous scale of ovule) (containing
(ovule- then seed-
group of plants, mainly shrubs, bearing structure) Wing Pollen tube female
but also including the scar (carries male gamete)
horizontally growing gamete from FERTILIZATION
Wing of seed pollen grain
welwitschia. derived from to ovum)
ovuliferous scale
Seed Seed
Microsporangium Seed
(structure in which Seed
pollen grains are Ovuliferous Wing
Seed scar
formed) Point of attachment scale
to axis of cone (ovule- then
OVULIFEROUS SCALE FROM seed-bearing
THIRD-YEAR FEMALE CONE structure) MATURE FEMALE CONE AND
WINGED SEED
Microsporophyll
(modified leaf
carrying Ovule
microsporangia) (contains Plumule Cotyledon
female (embryonic (seed leaf)
gametes) shoot)
Root
Bract
scale
GERMINATION OF
Scale leaf PINE SEEDLING
Axis
of cone Ovuliferous scale
(ovule- then seed- Axis
bearing structure) of cone
WELWITSCHIA
MICROGRAPH OF LONGITUDINAL MICROGRAPH OF LONGITUDINAL (Welwitschia mirabilis)
SECTION THROUGH YOUNG SECTION THROUGH SECOND-YEAR
MALE CONE FEMALE CONE

Frayed end of leaf

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