A New Concept of a Means of Speciation in Plants
TL;DR: L'importanza delle modificazioni cromosomiche del soma nel problema della speciazione delle piante che si riproducono vegetativamente si delinea.
Abstract: RIASSUNTOL'A delinea l'importanza delle modificazioni cromosomiche del soma nel problema della speciazione delle piante che si riproducono vegetativamente
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01 Jan 1971
TL;DR: In this paper, 154 plant species, chosen at random, and collected in the Netherlands were investigated cytologically, and the chromosome numbers determined were compared with data known from other countries.
Abstract: 154 plant species, chosen at random, and collected in the Netherlands were investigated cytologically. The chromosome numbers determined were compared with data known from other countries.
206 citations
01 Jul 1963
TL;DR: 154 plant species, chosen at random, and collected in the Netherlands were investigated cytologically and the chromosome numbers determined were compared with data known from other countries.
Abstract: 154 plant species, chosen at random, and collected in the Netherlands were investigated cytologically. The chromosome numbers determined were compared with data known from other countries.
134 citations
TL;DR: Two important evolutionary factors, hybridization and chromosome number variation, are discussed with respect to interactions involving clonal growth, vagility, and asexuality in aquatic angiosperms.
116 citations
70 citations
TL;DR: A great diversity in chromosome numbers as well as in chromosome size and constitution is found in the family Araceae.
Abstract: The chromosome numbers of 75 species belonging to the family Araceae have been determined. The numbers for 53 species are reported for the first time. One number differs from previous reports (Aglaodorum), and one number is corrected (Phymatarum). Within 15 genera (Gymnostachys, Pothoidium, Alloschemone, Heteropsis, Holochlamys, Anaphyllopsis, Dracontioides, Pseudohydrosme, Montrichardia, Bucephalandra, Taccarum, Asterostigma, Gorgonidium, Spathantheum and Ulearum) the chromosome numbers have not previously been determined. The total number of genera cytologically investigated is now 99 (c. 94%).
A great diversity in chromosome numbers as well as in chromosome size and constitution is found. The results are discussed in relation to the phylogeny and the previously published classifications of the family.
A total list of chromosome numbers counted (>700 species) in the Araceae is presented (Appendix).
58 citations
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01 Jan 1937
TL;DR: In this article, the authors present a taxonomy of diverse and diverse populations in the United States, including the following: 1.ORGANIC DIVERSITY 3 GENE MUTATION 15 MUTation as a basis for RACIAL and SPECIFIC DIFFERENCES 39 CHROMOSOMAL CHANGES 73 VARIATION in NATURAL POPULATION 118 SELECTION 149 POLYPLOIDY 192 ISOLATING MECHANISMS 228 HYBRID STERILITY 259 SPECIES AS NATUREAL UNITS 303 L
Abstract: ORGANIC DIVERSITY 3 GENE MUTATION 15 MUTATION AS A BASIS FOR RACIAL AND SPECIFIC DIFFERENCES 39 CHROMOSOMAL CHANGES 73 VARIATION IN NATURAL POPULATIONS 118 SELECTION 149 POLYPLOIDY 192 ISOLATING MECHANISMS 228 HYBRID STERILITY 259 SPECIES AS NATURAL UNITS 303 LITERATURE 323 INDEX 353
4,074 citations
TL;DR: Fragments are small in Rhoeo and in the tetraploids, showing that the assumption of pairing and crossing-over being restricted to the end regions is justified and that the anaphase in some forms comes to correspond with the hollow metaphase in others.
Abstract: 1. Fragments pair with major chromosomes inTradescantia by lateral chiasmata whose chromatid structure is revealed by pre-treatment. They do not then develop the usual major spiral. 2. Less contracted chromosomes in mutant cells have more coils. Spiralization therefore consists in reducing the number of coils. 3. Interlocked chromosomes, like multivalents, may have linear, twisted, or discordant orientations according to the method of interlocking. 4. The type of distribution of the bivalents on the metaphase plate inT. bracteata depends on the numbers of their chiasmata and on the radial or tangential adjustment of the individual bivalents. 5. The central chromosomes of the metaphase plate are pushed to the edge of the group during anaphase in some forms and species. This change may take place asymmetrically both at mitosis and meiosis. It shows that the repulsion from the poles is still acting on the chromosomes while they are moving towards the poles. Thus the anaphase in some forms comes to correspond with the hollow metaphase in others. 6.Rhoeo discolor and diploid, triploid and tetraploid species ofTradescantia show the results of inversion crossing-over under normal conditions. Fragments are small inRhoeo and in the tetraploids, showing that the assumption of pairing and crossing-over being restricted to the end regions is justified.
286 citations
TL;DR: Recent investigations utilization of the propriono or aceto carnmine smear technique and excised pretreatment with colchicine has given clear flat figures of the very long chromosomes of Lilium and allow a critical study of their morphology.
Abstract: THE GENUS Lilium has been investigated by numerous workers and all species are reported as having a somatic number of twenty-four (Sato, 1932; Sansome and LaCour, 1934; Mather, 1935; Beal, 1942; and Stewart, 1943) with the exceptions of the triploid species L. tigrinum .(Takenaka and Nagamatsu, 1930) and several species in which aneuploids are found (Sansome and LaCour, 1934; Mather, 1935; Beal, 1942; and Stewart, 1943). Thus, species relationships cannot be clarified by evidence of chromosome number. A similar situation obtains in many other genera and in these cases useful information can be obtained from a comparative study of the chromosome morphology of the members of the group. The earlier reports of clhroinosome number in Liliunm were based on observations of sectioned material. The limitations of this method for a study of clhromosome morphology on material with very long chromosomes such as Lilium are obvious. Cooper (1935, 1936) utilized pollen grain divisions in L. IIenr,yi and L. regale, but his illustrations show neitlher primary nor secondary constrictions. In recent investigations utilization of the propriono or aceto carnmine smear technique and excised pretreatment with colchicine (Stewart and Bamford, 1943; Emsweller and Stewart, 1944) has given clear flat figures of the very long chromosomes of Lilium and allow a critical study of their morphology. This is a report of such a study to serve as a base for more extensive investigations of the phylogeny of the genus. MIATERIALS AND METHODS.-Root tips were used exclusively and these were taken from bulbs obtained fro6m commercial dealers in the United States and fromii collections of native species and garden escapes in the vicinity of College Park. None of the planits used in previous studies survived the interval and plants reported here represent additional data on the occurrence of aneuploids in Lilium (Stewart, 1943). Identification has been checked witlh Elwes (1880), Wilson (1925), Woodcock and Coutts (1935), Slate (1939), and various articles in the Royal Horticultural Society Lily Yearbooks. Root tips were fixed in 3:1 absolute alcoholglacial acetic acid for 24 hours, then rinsed and stored in 80 per cent alcohol until used. Smears were made by the propriono-carmine technique. The oiiiission of acid hydrolysis and the use of glass tools throughout to eliminate any trace of iron in the stain resulted in the nucleoli staining a bright red color from 24 to 48 hours after the preparation of the slide. The roots prepared in this way showed cells at the critical stages of mitosis for the classification of constrictions as shown in fig. 49 and 51. 1 Received for publication July 16, 1946. Scienitific Paper No. A-135. Contribution No. 2024 of the Maryland Agricultural Experiment Station (Departm ant of R3otany). The morphology of the chromosomes at somatic metaphase was determined from divisions in root tips given excised pretreatment for 30 minutes in a 0.2 per cent aqueous solution of colchicine followed by washing in water for 90 minutes. This is a slight modification of previous methods (Burrell, 1939; O'Mara, 1939; Stewart and Bamford, 1943; Stewart, 1943; Emsweller and Stewart, 1944). Buds and mature pollen have been collected and preserved for future work. Observations were made with the aid of 43x and 90x apochromatic oil immersion objectives and 15x compensating oculars. Camera lucida drawings at table level (approximately 2000X) were made of all the metaphase clhromosomes separately in from one to three cells of each plant of a species or variety. These were cut out and for each cell arranged in pairs on the basis of total length, position of primary constriction, and number and position of secondary constrictions. The idiograms (fig. 1-48) are these drawings of a haploid set from a typical cell which was the least distorted in preparation and traced so that the primary constrictions appear on a horizontal line. The order from left to right in each case is of increasing arm length ratio (long/ short) rising from approximate unity. Letters are assigned to the chromosomes according to their order in this scheme. Both chromosomies of pairs which are heteromorphic in the position of the secondary constrictions are shown and designated by a letter and its prime. The centric fragments and extra chromosomes which are not duplications of one of the normal complement are placed on the right regardless of the length of its short arm and are designated by the letter MI. In addition to the camera lucida idiograms a series of photoidiograms of representatives of the divisions of the genus Lilium are presented (fig. 52). These are constructed in exactly the same way as the other idiograms except that photomicrographs are used in place of camera lucida drawings. RESULTS.-The results are presented almost completely by the idiograms (fig. 1-48). There are nio large variations in chromosome morphology in the genus, all species having two long pairs of chromosomes with submedian centromeres and ten pairs with subterminal centromeres. The 2n number of all species reported here is 24 and although individuals were found in L. auratum, L. tsingtauense, L. Sargentiae, and L. pumilum with 2n 25 and one plant in L. Henryi with 2n 26, the additional chromosomes are, with two exceptions, centric fragments and in all cases are unlike any of the normal complement. However, the variations in the length of the chromosomes and the variation in position and function of the constrictions differentiate the species into two groups. The following is a detailed classification of the
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70 citations
TL;DR: RIASSUNTOVengono riportati i cartogrammi di ventotto specie, appartenenti a quindici generi di Araceae spontanee e coltivate, la cui propagazione avviene generalmente per via vegetativa e viene tracciata la loro probabile derivazione filogenetica da un numero base x=7.
Abstract: (1955). Cytology of Different Species of Aroids with a View to Trace the Basis of their Evolution. Caryologia: Vol. 7, No. 2, pp. 221-291.
52 citations