“…1 to 3). However, the great majority of the nucleoli observed showed a number of lighter spaces of various sizes the largest of which might possibly correspond to the vacuoles previously reported (9)(10)(11)(12)(13)21). Although some of these light spaces appear structureless, if not empty, they are not necessarily so in the living 782 NUCLEOLUS IN MERISTEMATIC CELLS state: their content is probably extracted during the preparation procedures.…”
Interphase nucleoli from Vicia faba and Allium cepa meristematic cells are roughly classified into two categories: (a) those that commonly show a rather homogeneous texture (except for small light spaces of various sizes) and frequently contain dense particles 140 A in diameter; (b) those found more frequently in Vicia characterized by a very sharp boundary between a dense outer cortex and a much fighter central core. The dense particles are not found in such nucleoli. In Allium the boundary is more irregular and dense particles are sometimes observed in the outer layer. Many nucleoli show a structure intermediate between these two types. They are characterized by a gradient of increasing density from the center to the periphery and occasionally contain dense 140 A granules.During interphase, certain nucleoli are closely associated with segments of chromatin strands which undoubtedly represent nucleolar organizing regions.The dense 140 A granules are followed during the mitotic cycle. In Allium,
“…1 to 3). However, the great majority of the nucleoli observed showed a number of lighter spaces of various sizes the largest of which might possibly correspond to the vacuoles previously reported (9)(10)(11)(12)(13)21). Although some of these light spaces appear structureless, if not empty, they are not necessarily so in the living 782 NUCLEOLUS IN MERISTEMATIC CELLS state: their content is probably extracted during the preparation procedures.…”
Interphase nucleoli from Vicia faba and Allium cepa meristematic cells are roughly classified into two categories: (a) those that commonly show a rather homogeneous texture (except for small light spaces of various sizes) and frequently contain dense particles 140 A in diameter; (b) those found more frequently in Vicia characterized by a very sharp boundary between a dense outer cortex and a much fighter central core. The dense particles are not found in such nucleoli. In Allium the boundary is more irregular and dense particles are sometimes observed in the outer layer. Many nucleoli show a structure intermediate between these two types. They are characterized by a gradient of increasing density from the center to the periphery and occasionally contain dense 140 A granules.During interphase, certain nucleoli are closely associated with segments of chromatin strands which undoubtedly represent nucleolar organizing regions.The dense 140 A granules are followed during the mitotic cycle. In Allium,
“…Later, the chromosomes of the pairs round up, yet the pairs retain a somewhat definite arrangement in the nucleus (PI. In different species of Oenothera, however, as described especially by Cleland (1922), the single chromosomes are attached end to end during the heterotypic division in a continuous ring (or rings), the number in the ring varying with the species, and alternate chromosomes pass to each pole. 51).…”
Section: Development Of the Microspore Mother Cellmentioning
“…There is every reason to believe (CLELAND 1928;CLELAND andOEHLKERS 1929, 1930) that these alterations in linkage are based upon the chromosome configuration which happens to be present in any particular complex-combination. P and R, for instance, belong as a rule in different chromosomes.…”
“…It was in Oenothera that the presence of such circles was first described (CLELAND 1922(CLELAND , 1923, and circles of definite size are preeminently characteristic of this genus. They have subsequently been found, however, in other genera of plants as well.…”
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