. Embryogenesis in plants. Embryology. EMBRYOGENESIS IN GYMNOSPERMS 183 organising capacity of the distal embryo apex may be discerned. Chamberlain records that the living suspcnsor in Ceratozamia can be pulled out to a length of some 7-8 cm, Polyembryony within a single archegonium has also been observed, in Macrozamia reidlei, there may be one to three additional lateral embryos. These arise like the main embryo, each owing its formation to a small group of actively dividing cells at the basal periphery of the. Fig. 40. Dioon edule Embryo in longitudinal section, showing an early stage
. Embryogenesis in plants. Embryology. EMBRYOGENESIS IN GYMNOSPERMS 183 organising capacity of the distal embryo apex may be discerned. Chamberlain records that the living suspcnsor in Ceratozamia can be pulled out to a length of some 7-8 cm, Polyembryony within a single archegonium has also been observed, in Macrozamia reidlei, there may be one to three additional lateral embryos. These arise like the main embryo, each owing its formation to a small group of actively dividing cells at the basal periphery of the. Fig. 40. Dioon edule Embryo in longitudinal section, showing an early stage in the formation of cotyle- dons. The enlarged basal region is the coleorhiza. The shoot and root apical meristems are not yet clearly differentiated (after Chamberlain). proembryo. The primary suspcnsor may also fork and give rise to equal embryos. A similar branching of the suspcnsor has also been seen in Encephalartos. The Embryo. Contemporaneously with these suspcnsor develop- ments, the embryonic region has been growing slowly. The differentia- tion of the rather uniform mass of meristematic cells takes place very gradually, but two cotyledons are eventually formed, while below them, in the bulky basal region known as the coleorhiza, an endogenous root has its inception, Fig. 40. In the early stages of this embryonic development, when the whole of the apical region is still growing, both periclinal and anticlinal divisions take place in the cells of the outermost tissue. The distal, superficial layer, which by virtue of its position becomes the dermatogen, appears to assume a haustorial function, Fig. 40, but whether the main nutrition of the embryo is by way of this tissue region, or acropetally by way of the suspcnsor, is still a matter for conjecture. After the formation of the cotyledons, the sunken shoot apex gives rise to the first leaf and to one or more associated. Please note that these images are extracted from scanned page images that may have been digitally enh
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Keywords: ., bookcentury1900, bookcollectionbiodiversi, booksubjectembryology
