. Embryogenesis in plants. Embryology. EMBRYOGENESIS IN GYMNOSPERMS 179 with the upper and lower regions of the zygote. Division of nuclei of the lower group is always accompanied by division in the upper group but the converse is not always found. From this it could be inferred either that there is a gradient of a stimulatory substance from the archegonium. Fig. 38. Fertilisation in Dioon edule Reconstruction of an ovule, as seen in longitudinal section, with its prothallus and two of the archcgonia at the time of fertilisation. Motile spermatozoids are dis- charged from the ends of the polle
. Embryogenesis in plants. Embryology. EMBRYOGENESIS IN GYMNOSPERMS 179 with the upper and lower regions of the zygote. Division of nuclei of the lower group is always accompanied by division in the upper group but the converse is not always found. From this it could be inferred either that there is a gradient of a stimulatory substance from the archegonium. Fig. 38. Fertilisation in Dioon edule Reconstruction of an ovule, as seen in longitudinal section, with its prothallus and two of the archcgonia at the time of fertilisation. Motile spermatozoids are dis- charged from the ends of the pollen-tubes into the archegonial cavity. A sperm has entered the egg on the left; the egg on the right still shows the ventral canal nucleus; two sperms, immediately above, are ready to enter this egg (after Chamberlain). base to the neck, or that there is a gradient of inhibitory substance in the opposite direction. During the earlier phase of zygotic development many more nuclei are to be observed at the upper end. The extent of free nuclear formation varies in different genera and species. In the large ovum of Dioon edule, which may be as much as 5 mm long, some 1000 nuclei are present (the corresponding theoretical number would be 1024); in Zaimafloridaiia, with a 3 mm ovum, 256 nuclei have been. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wardlaw, C. W. (Claude Wilson), 1901-. London, Methuen; New York, Wiley
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Keywords: ., bookcentury1900, bookcollectionbiodiversi, booksubjectembryology
