Author
Frank H. Smith
Bio: Frank H. Smith is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Brodiaea & Corm. The author has an hindex of 4, co-authored 4 publications receiving 52 citations.
Papers
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TL;DR: The increasing number of descriptions of nuclear divisions in tapetal cells has established the fact that these divisions are mitotic rather than amitotic, as was previously considered by many to be the case.
Abstract: The increasing number of descriptions of nuclear divisions in tapetal cells has established the fact that these divisions are mitotic rather than amitotic, as was previously considered by many to be the case. Strasburger (I882) described typical mitoses of tapetal nuclei. Duggar (I899) also early described mitoses in the tapetal cells of Bignonia venusta, which are normally binucleate during the stages of microsporogenesis following synizesis. Tischler (I906) described mitotic division of the nuclei in tapetal cells of Ribes. The second nuclear division, however, he found to be amitotic. He also found nuclei with the tetraploid chromosome number and concluded that such nuclei resulted from a fusion of the two diploid nuclei formed after the first division. Winkler (i906) described a fusion of nuclei in the tapetal cells of Wikstroemia indica. Mitotic divisions occur in the tapetal cells, resulting in a 2-6 nucleate condition. These nuclei usually fuse to form giant nuclei, but in some cases they remain separate. Tahara (I9IO) found in Morus indica that during the early stages of the heterotypic division the tapetal cells are binucleate. Their nuclei may fuse to form a single tetraploid nucleus which in turn may divide mitotically, or they may divide separately to form four nuclei. The four nuclei then fuse in pairs, so that each cell contains two tetraploid nuclei which may later divide mitotically. Bonnet (I912) made an extensive study of the tapetal cells in several genera of angiosperms and found mitosis to be the only method of nuclear division in the material examined. In Yu,cca the first tapetal nuclear division occurs before synizesis; in Fuchsia it occurs after synizesis. The second divisions are simultaneous in each cell. In some cases two of the spindle poles converge, so that during the telophases two of the four daughter nuclei fuse to form a single tetraploid nucleus. Thus the cell contains one tetraploid and two diploid nuclei. Bonnet also described a fusion of nuclei in a resting condition which results in the formation of tetraploid and octoploid nuclei. Gates and Rees (192I) found only mitotic nuclear divisions in the tapetal cells of Lactuca. The first division occurs at the start of synizetic contraction, and by the time of maximum synizetic contraction the tapetal cells are all binucleate. Some of them remain binucleate; others undergo a second nuclear division as the pollen mother cells reach the open spireme stage. The
18 citations
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TL;DR: A general survey of the cormous monocotyledon, found in low meadows from California to British Columbia, which produces a new corm each year immediately above the old one and has contractile roots provided in the axils of the leaves.
Abstract: Brodiaea lactea (Lindl.) Wats. (B. hyacinthina var. lactea Baker; Hookera hyacinthina (Lindl.) Kuntz.) is found in low meadows from California to British Columbia. It produces a solid corm which varies from 7 to 50 mm. in diameter and is covered with a very heavily lignified sheath. The flower stalk, which is 30-80 cm. tall, bears numerous white, open-campanulate flowers in a several-bracted umbel. The mature corm carries two linear-lanceolate leaves which are 5-8 mm. broad and somewhat shorter than the flower stalk. Like many of the cormous monocotyledons, it produces a new corm each year immediately above the old one. Offsets, provided with contractile roots, are also produced in the axils of the leaves. The contractile roots of these offsets have proved of such interest that in this study emphasis has been placed upon their development. The consideration of the corm has been limited to a rather general survey of its seasonal development.
17 citations
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TL;DR: The nucleolus is organized in the telophase through the activity of a distinct deep-staining body having a definite position in one chromosome (the satellited chromosome) of the monoploid complement through a reciprocal translocation which broke this body into two parts.
Abstract: 1.
The nucleolus is organized in the telophase through the activity of a distinct deep-staining body having a definite position in one chromosome (the satellited chromosome) of the monoploid complement. Correlated with the number of satellited chromosomes present, the telophases of somatic tissue of haploids show one nucleolus, diploids, two nucleoli and triploids, three nucleoli. That the nucleolus develops through the activity of this body (refered to as the nucleolar-organizing body or element) was obtained from a reciprocal translocation which broke this body into two parts. Both interchanged chromosomes possessed a section. Nucleoli developed from each of these two segments. Thus, plants homozygous for the interchange developed four nucleoli in their somatic telophases; plants heterozygous for the interchange developed three nucleoli in their somatic telophases. Similarly, the telophase nucleoli resulting from the first division within the monoploid microspore of normal diploids show only one nucleolus, whereas, those of plants homozygous for the interchange are characterized by the development of two nucleoli.
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The functional capacity to develop a nucleolus is not the same for both segments of the severed nucleolar-organizing body. This is evident when the two interchanged chromosomes are present in the same nucleus. The segment of the nucleolar-organizing body possessed by one interchanged chromosome produced a large nucleolus, whereas, the segment of the nucleolar-organizing body possessed by the other interchanged chromosome produced a small nucleolus. When this latter chromosome, with the nucleolar-organizing element of slower rate of functional capacity is present without the former (i. e. without a competing nucleolarorganizing element) it produces, in contrast, a large nucleolus.
3.
The activity of the nucleolar-organizing element is hindered by certain genomic deficiencies. When this occurs, many small nucleolarlike bodies are produced and remain associated with the other chromosomes of the complement. These small nucleoli appear to develop from a swelling and later collection into droplets of the matrix substance of the chromosome.
589 citations
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TL;DR: A discussion of how translocations have been and how they might be used as tools in the investigation of other cytological and cytogenetic problems and also certain applications to practical breeding have been included.
Abstract: The foregoing survey of the literature shows that translocations are of wide-spread occurrence in plants. Most of them have been found in the angiosperms: in 49 genera of dicots and 47 genera of monocots; but some have been reported in the gymnosperms (in two genera), also in the fungi. Studies at meiosis will undoubtedly reveal translocations in many other species, either in occasional plants or in different groups isolated geographically. In certain cases they seem to have played a part in the evolution of present karyotypes. In a number of cases, the presence of translocations has not been definitely established, but they are one possible explanation of the observed configurations. The survey reveals the need for additional detailed studies of interchanges. What accounts for directed segregation in the interchange rings in certain species? For each of the factors which has been suggested there is one or more species which does not behave in the predicted manner. Experimentally produced interchanges in other species having these features would be useful; also in species having directed segregation of the sex chromosomes. A discussion of how they have been and how they might be used as tools in the investigation of other cytological and cytogenetic problems and also certain applications to practical breeding have been included.
199 citations
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TL;DR: The most common mechanism of polyploidization acting in plant tissues and cells appears to be supernumerary chromosome reproduction, which is responsible for polysomaty in root and shoot meristems as well as forpolyploidy in any type of differentiated tissues and for nuclear growth in general.
Abstract: SUMMARYThe actually available data on the occurrence of polyploidy in plant tissues and cells have been critically reviewed. The incidence of polyploidy in the plant body, the cytological mechanisms by which the polyploid condition is produced, the physiological and general significance of polyploidy in the « soma » of plant organisms and related questions have been considered.The most common mechanism of polyploidization acting in plant tissues and cells appears to be supernumerary chromosome reproduction. This is responsible for polysomaty in root and shoot meristems as well as for polyploidy in any type of differentiated tissues and for nuclear growth in general. During the development of ephemeral tissues, such as the anther tapetum, supernumerary chromosome reproduction has been sometimes found to occur intermingled with monochromosome mitoses and/or typical endomitosis of the Gerris-type.Abortive mitoses due to spindle disturbances and chromosome stickiness or both are a very common polyploidization...
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119 citations
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TL;DR: Nachdem 1873, 1875 and 1882 SCHNEIDER, STRASBVRGER, BtiTSCHLI and FLEMMING die kleinen bei den Kernteilungen auftretenden St~bchen gefunden hatten, beobachtete S. NAWASCHIN 1912 bei zwei untersuchten Arten einiger Chromosomen kleine K5rperchen,
Abstract: Nachdem 1873, 1875 und 1882 SCHNEIDER, STRASBVRGER, BtiTSCHLI und FLEMMING die kleinen bei den Kernteilungen auftretenden St~bchen (die wir seit WALDEYER 1888 als Chromosomen bezeichnen) gefunden hatten, beobachtete S. NAWASCHIN 1912 bei zwei yon ihm untersuchten Arten (Galtonia candicans und Muscari tenui/lorum) an den Enden einiger Chromosomen kleine K5rperchen, die durch einen Faden mit den Cbromosomen verbunden sind. Diese Gebilde bezeichnete er als Trabanten oder Satelliten und beschreibt sie sp~ter auch bei Albuca (1913), Fritillaria imperialis (1916) und Epipactis palustris (yon M. NAWASCHIN 1925 mitgeteilt). Nach S. NAWASCHINs Entdeckung fing man an, diesen kleinen bei einigen Chromosomen gefundenen Anh~ngseln Aufmerksamkeit zu schenken, und bald wurden auch bei verschiedenen anderen Pflanzen Trabanten gefunden. 1925 faBte M. NAWASCHrN alle diesbezfiglichen Angaben zusammen: 13 Jahre nach der Entdeckung der Trabanten waren diese bei 63 Arten aus 23 verschiedenen Gattungen (nur Phanerogamen) festgestellt. Die Untersuchungen nahmen weiter zu, und bis 1928 sind nach KUHN Trabanten bei 130 Arten aus 38 verschiedenen Gattungen festgestellt worden. Diese weite Verbreitung der Trabanten fiel sowohl M. NAWASCHIN als auch KtrHN auf. M. NAWASCmN (1925) sagt, dab sie bei den h6heren Pflanzen sehr oft vorkommen und denkt, ,,dab diesen r~tselhaften Gebilden eine doch nicht unbedeutende Rolle im Pflanzenreich geh6rt\". Eine Beziehung zwischen Trabanten und Nucleolen in der Prophase und im ruhenden Kern wurde yon S. NAWASCHIN 1913 bei Galtonia candicans bemerkt. Er beobachtete, dab die Trabanten in dem ruhenden Kern auf dem Nucleolus sitzen, yon dem sie in der Prophase von den Chromosomen abgehoben werden sollen. Eine Reihe yon Autoren hat
66 citations