Other Conifers

Some conifers don't produce woody seed cones with conspicuous scales, nor do all produce both pollen and seed cones on the same plant. For example, yew (Taxus) and California nutmeg (Torreya) produce ovules singly at the tips of short axillary

Pollen Chamber Pine

micropyle pollen chamber integument (2n)

nucellus archegonium egg female gametophyte (n)

Figure 22.7 A longitudinal section through part of a pine ovule, x100.

Introduction to See d Plants: Gymnosperms 427

embryo.

embryo.

Megasporangium And Female Gametophyte

ovule (contains megasporangium)

microsporocytes undergo meiosis, producing zygote develops into the embryo of a seed megasporocyte undergoes meiosis, producing ovule (contains megasporangium)

zygote develops into the embryo of a seed

Zygote Develops Into Embryo

pollen tube grows toward an archegonium;' a sperm unites with an egg, forming a zygote within the archegonium three megaspores degenerate; the fourth develops into a female gametophyte

Megaspores And Microspores
microsporangium

microsporocytes undergo meiosis, producing pollen tube grows toward an archegonium;' a sperm unites with an egg, forming a zygote within the archegonium male gametophyte male gametophyte female gametophyte microspores megasporangium three megaspores degenerate; the fourth develops into a female gametophyte microspores pollen grain wing generative cell tube cell

(spermatogenous cell divides, producing two sperms

(spermatogenous cell divides, producing two sperms spermatogenous cell sterile cell pollen tube tube nucleus generative cell 'divides, producing two more cells pollen grain wing generative cell tube cell spermatogenous cell sterile cell pollen tube tube nucleus

Figure 22.8 Life cycle of a pine.

shoots. Each ovule is at least partially surrounded by a fleshy, cuplike covering called an aril. In yews, this is bright red and open at one end, giving the fleshy seed the appearance of a small red hors d'oeuvre olive with its stuffing removed (Fig. 22.9). The seeds with their fleshy arils are produced only on female plants, while the pollen cones are produced only on male plants.

Podocarps are conifers of the Southern Hemisphere and are widely planted as ornamentals in regions with milder climates. Their fleshy-coated seeds are produced singly and are similar to those of yews. They are not, however, open at one end and have an additional larger appendage at the base (Fig. 22.10). The origin of these fleshy seeds is not clear and has led to speculation that yews and podocarps may have diverged from other conifers very early in the evolution of gymnosperms.

The scales of the seed cones of junipers tend to be fleshy at maturity, and they look more like berries than cones. Juniper pollen grains, as well as those of a number of other

428 Chapter 22

Conifers Flowering Plants

cones and are surrounded at maturity by a red, fleshy, cuplike structure called an aril.

Figure 22.10 Fleshy seeds of a podocarp (Podocarpus). Note the large appendage at the base of each seed.

cones and are surrounded at maturity by a red, fleshy, cuplike structure called an aril.

conifers, do not have air sacs. Cypress and redwood seed cone scales are flattened at the tips and narrow at the base, where they do not overlap one another as do pine cone scales.

The two California species of redwoods are both renowned for their size, height, and longevity. Coastal redwoods occasionally grow to a height of 90 meters (295 feet), and one tree in Humboldt County, California, is 111.6 meters (366.2 feet) tall; it is believed to be the tallest conifer in the world. The other species, usually referred to as Big Tree or Giant Redwood, is confined to the western slopes of California's Sierra Nevada range. It does not grow quite as tall as the coastal redwood but exceeds it in total mass. The General Sherman tree in Sequoia National Park, for example, is 31 meters (101.5 feet) in circumference at the base and over 24 meters (79 feet) in circumference 1.5 meters (5 feet) above the ground. It weighs an estimated 5,594 metric tons (6,167 tons). There are 600,000 board feet of timber in this single tree—enough to build more than 75 five-room houses (although the wood is generally not suitable for

Figure 22.10 Fleshy seeds of a podocarp (Podocarpus). Note the large appendage at the base of each seed.

construction purposes) or to make 20 billion toothpicks. It is over 3,500 years old.

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Responses

  • Kaelyn McLean
    Do podocarps have an aril?
    8 years ago
  • vanessa sch
    What conifers and plants?
    8 years ago
  • Kinfe Fesahaye
    Which conifers do not have woody seed cones?
    7 years ago
  • welde
    What are examples is both flowering plants and conifers?
    7 years ago

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