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Polyembryony Among Abietineae
John T. Buchholz
Vol. 69, No. 2 (Feb., 1920), pp. 153-167
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2469345
Page Count: 15
1. Although all species of Pinus have shown a complete separation of the 4 primary embryos, this feature of cleavage polyembryony is not characteristic of all Abietineae. 2. The cleavages which separate the 8 embryos from each other are the free nuclear divisions of the proembryo. In forms without cleavage polyembryony (Picea, and as far as we know concerning other forms), cell divisions homologous with those in Pinus occur in the proembryo. 3. The embryos of the Abietineae may be arranged in an intergrading series, with Pinus at one end and Pseudotsuga at the other, on the basis of the occurrence of cleavage polyembryony, rosette embryos, and the apical cell. The rosette embryos and their vestiges, the rosette cells, are gradually eliminated as we pass from Pinus to Pseudotsuga. 4. Cleavage polyembryony, rosette embryos, and the apical cell mark a primitive type of embryo development. 5. The embryo development of this group shows how the apical cell was lost in the evolution of the Abietineae. 6. On the basis of embryogeny Pseudotsuga is unique and is entitled to rank as a separate genus.