Origin of the Coleorhiza in Cycad Seedlings and its Structural Homology with That of the Poaceae |
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Authors: | Hannes P J Robbertse Nat Grobbelaar Elsa du Toit |
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Institution: | (1) Department of Plant Production and Soil Science, University of Pretoria, Pretoria, 0001, South Africa;(2) Department of Botany, University of Pretoria, Pretoria, 0001, South Africa |
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Abstract: | In the literature there is disagreement about the existence of a coleorhiza in cycad embryos. In this paper the terminology
of the cycad ovule, seed and embryo is revised. It was confirmed that the cycad ovule and seed are pachychalazal and that
the seed coat is exclusively formed by the pachychalaza. The term ‘pleurotesta’ as a substitute for the so-called ‘endotesta’
is suggested to describe the inner, membranous part of the seed coat. The anatomy of the cycad embryo was studied in comparison
with the grass embryo and it was found that a coleorhiza does exist in cycad embryos and derives from the distal part of the
suspensor. It is postulated that the coleorhiza in grasses also derives from the distal part of the suspensor and that the
two structures are therefore structurally homologous. |
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