. Morphology of gymnosperms. Gymnosperms; Plant morphology. GNETALES 399' thirty-two at the time of observation), the basal ones of which develop numerous embryonal tubes that surround the lower part of the sus- pensor, while the terminal ones (a plate of eight cells) develop the embryo (fig. 454). The embryonal tubes are produced from the same region that develops as a secondary suspensor in Ephedra, but their function is not the same. In germination the young seedling of Welwitschia (Bower 6,7) shows a well-developed root, a very long hypo- cotyl, and two small cotyledons; and between the ro
. Morphology of gymnosperms. Gymnosperms; Plant morphology. GNETALES 399' thirty-two at the time of observation), the basal ones of which develop numerous embryonal tubes that surround the lower part of the sus- pensor, while the terminal ones (a plate of eight cells) develop the embryo (fig. 454). The embryonal tubes are produced from the same region that develops as a secondary suspensor in Ephedra, but their function is not the same. In germination the young seedling of Welwitschia (Bower 6,7) shows a well-developed root, a very long hypo- cotyl, and two small cotyledons; and between the root tip and the hypocotyl there is de- veloped a very conspicu- ous footlike ("spade- like," 28) process that remains in the seed as a haustorial organ. At a later stage the cotyledons become more conspicu- ous, and the single pair of persistent leaves ap- pears associated with them (fig. 455). The embryo-forma- tion of Gnetum is a repeti- tion of that of Welwit- schia, at least in general outline. Lotsy's account (15) for Gnetum Gnemon describes the extensive suspensor-like elongation of the ferti- lized egg, the penetration of the endosperm in various directions, the occasional branching of the tube, and the cutting-off of the embryo cell, but does not follow the nuclear divisions. A recent investigation (25) of the same species has added some interesting details. When the endosperm is fully developed, having replaced the nucellus completely during the second season, its pe-. FiG. 455.—Welwitschia mirabilis: a young seedling, showing the cotyledons and the pair of persistent leaves; the bilobed crown is evident just above the insertion of the cotyledons; natural size. —From photograph by H. 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 Coulter, John Merle, 1851-1928; Chamberlain, C
Size: 1410px × 1773px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisherchicagouniversityo
