Profound changes in climate, glaciation and finally widespread desertification are linked to the tectonic assembly of the supercontinent Pangaea. Conifers, gingkos and cycads — naked-seed, "cone-bearing" trees — and dry-tolerant spore ferns replace the dying lush Carboniferous forests. Wind carries pollen from tree to tree, a common pollination method before some animals begin to provide the service.
Cycads grow well in soils extremely low in nitrogen. Cyanobacteria, living in the roots where they induce a special layer of tissue, convert nitrogen from the air to a form usable by the cycad.
University of Montana--Missoula. Environmental Studies Program
© 1997 Stiftung Drittes Millennium
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Liebes, Sid; Mittelstadt, Laurie; Waugh, Barbara; and Brynes, Lois, "Panel 67: Sowing And Reaping" (1997). A Walk Through Time - From Stardust To Us. 67.