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Unformatted text preview: ther spirally, in opposite pairs or in whorls of 3 or 4 On young plants, the leaves are needle-‐
like, becoming small and scale-‐like on mature plants of many genera Female cones small, either woody or “berry-‐like” Includes: cypress, junipers, thuja, redwood (largest trees, up to 115 m) “Short-‐shoots”: needles in bundles Needles retained for 2-‐4 or more years Pine needles adapted to dry condi�ons Secondary growth begins early Epidermis
(waxy cuticle) Resin duct sunken stomata Fig. 18-14 Cedrus atlantica Other conifers: Yew family (Taxaceae) Many-‐branched, small trees and shrubs Leaves are spirally arranged, o�en twisted at the base to appear 2-‐
ranked Plants are dioecious Ovuliferous scale develops into a ﬂeshy aril partly enclosing the seed (not a fruit!) Bird dispersed Seeds and leaves toxic! Other conifers: Araucaria family (Araucariaceae) Ancient family of conifers Now only found in the Southern Hemisphere Horizontal, spreading branches grow in whorls Several species are popular ornamental trees (monkey-‐
puzzle tree, Norfolk Island pine) 6 Male sporangia and gametophyte Conifer (pine): reproduc�on Sporophylls are born on cones (strobili) Male cones: simple with short unbranched axis that bears microsporophylls Female cones: compound with short axis bearing cone bracts Male and female cones on same tree (conifers) female male Microsporophylls bear 2 microsporangia Each microsporangium contains many sporocytes Each microsporocyte produces 4 haploid microspores (meiosis) Each microspore develop into a pollen grain (male gametophytes) No antheridium! Pollen grain Fig. 18-22 Microsporangium with microspores Reduc�on in size of gametophytes prothallial cells
generative cell Pinus pollen grain, 4-‐celled, ca. 40 um No longer free living tube cell
wings Fig. 18-18a Female sporangia and gametophyte (conifers) Female (ovulate) cones larger and more complex than pollen-‐bearing cones Reduced branch systems (seed-‐scale complexes) Megasporophylls are fused into an ovuliferous scale that bears two ovules Horsetail gametophyte (bisexual), mul�cellular, ca. 3 mm Free living 7 Female sporangia and gametophyte (conifers) Megasporocytes are cells contained within the ovule Produce four megaspores by meiosis Three of the megaspores die The re...
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