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Unformatted text preview: maining one develops into a female gametophyte within the megasporangium (nucellus) Female gametophytes produce eggs within archegonia micropyle Integument
Megasporocyte (2n) Pine life cycle Alterna�on of genera�ons (diploid/haploid) Life cycle span 2 years (pine) ♂ Spring, yr1 Megaspores (n) ♀ 6-12 mo Megaspore Megagametophyte
(endosporic) Archegonium with egg Pollina�on The pollen grains are released from the sporophyte and transferred to the vicinity of the egg Wind Outcrossing Large amounts of pollen yr2
(15 mo) Autumn, yr2 Pine life cycle: pollina�on Two wing-‐like structures on the pollen grain aid the pollen to be carried by wind The male gametophyte 4-‐celled: genera�ve cell and tube cell (and 2 prothallial cells) The genera�ve cell divides to produce two sperm cells The tube cell grows toward the egg, producing a pollen tube 8 Pine life cycle: fer�liza�on Sperm transferred directly through the pollen tube to the egg The two sperm cells are released and move toward the egg Eggs in archegonia One sperm nucleus unites with the egg nucleus (the other degenerates) Sperm non-‐mo�le (water is not required for reproduc�on) Other gymnosperms: Cycads Palm-‐like plants, but true secondary growth Mainly tropical-‐subtropical (Zamia pumila na�ve to Florida) Plants are dioecious (seed cones and pollen cones) Mul�ﬂagellated sperm Specialized pollina�on (insects) Harbor cyanobacteria (nitrogen ﬁxa�on) O�en highly toxic (but starch used as food) Pine life cycle: seed development Zygote develops into a suspensor and proembryo (polyembryony – only one survives) Seed: – Integuments (and remnants of nucellus) develop into seed coat – Gametophyte (food reserve) – Embryo: root-‐shoot axes, cotyledons (several) Cones mature and seeds are dispersed The seed is the dispersal unit! scale seeds Other gymnosperms: Gingko Only 1 species, Gingko biloba (China) “Living fossil” (270 my) -‐ no na�ve popula�ons? Important cul�var, tolerate pollu�on Short shoots/long shoots Unique fan-‐shaped leaves, deciduous Dioecious (no cones) Mul�ﬂagellated sperm Fleshy coated seeds (smelly!) Medicinal uses 9 Other gymnosperms: Gnetophytes Monophyle�c but diverse group Gnetum: trees and vines with leathery Introduc�on to...
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