The morphology of the dormant embryo and young seedling of five species of Dioscorea from Nigeria

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SUMMARY.

The family Dioscoreaceae belongs to the group of plants termed the monocotyledons on account of the single seed leaf. As expected, investigation of the developing seedling showed one cotyledon acting as an absorptive organ in the endosperm of the seed. The first leaf above ground was not of the new shoot, as this arose very much later, apparently separated from this first leaf. The first leaf was present as a very small scale-like structure, opposite the absorptive cotyledon, in the seed. On germination, it is carried out of the seed by the elongation of the absorptive cotyledon stalk so that it develops its full structure outside the seed. It is shown that the bud that gives rise to the plumule arises in the angle formed by the petiole of the first leaf and the stalk of the absorptive cotyledon. It is also shown that the vascular traces in the petiole of the first leaf combine with those of the cotyledon in the hypocotyl, from where they pass to the radicle.

It is suggested that there are two cotyledons in Dioscorea bulbifera L., D. praehensilis Benth., D. odoratissima Pax., D. hirtiflora Benth., D. preussii Pax., one of which remains in the seed as an absorptive organ. The other, the emergent cotyledon, developing late, appears above ground and carries out the normal photosynthetic functions of a leaf.

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