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Opuntia series Armatae is evaluated considering morphological (vegetative, floral, and carpological) and cytogenetical (diploid number, presence of heterochromatin, and physical localization of ribosomal genes) features to shed light on their systematics and evolution. Three complexes (named O. elata, O. megapotamica, and O. monacantha) are proposed to accommodate seven species according to the tepal, fruit, stigma, and seed aril traits. Additional systematic conclusions include the following: (i) O. stenarthra, O. assumptionis, O. cognata, and O. subsphaerocarpa are synonyms; (ii) O. elata is a variable species with two varieties (var. cardiosperma and var. obovata); (iii) O. rioplatense is a synonym of O. elata var. obovata; and (iv) O. megapotamica is a polymorphic species with two varieties (one newly described and a new combination). All species had small similar-sized symmetrical chromosomes and were tetraploid (2n = 44), except for a population of O. arechavaletae and O. monacantha (2n = 22). All showed one or two pairs with CMA+/DAPI− NOR associated bands. The 18–5.8–26S rDNA loci seem to coincide with CMA+/DAPI−/NOR blocks. The number of 5S signals detected was proportional to the ploidy level of the species. A combination of cytogenetic and morphological features helped to differentiate the complexes, species, and varieties of Opuntia ser. Armatae.

The higher magnifications and resolution possible with scanning electron microscopy can provide more detailed information on chromosome morphology than light microscopy. However, overlying cell debris can obscure surface details. A method is described whereby standard organic acid–alcohol fixatives and slightly modified techniques of routine plant chromosome squash preparations can be used to provide samples of mitotic and meiotic chromosomes of wheat suitable for examination by scanning electron microscopy.Key words: scanning electron microscopy, light microscopy, wheat, chromosomes.

Interspecific hybrids were successfully produced, using embryo culture, between Eurasian and American species of Bromus section Pnigma. Cytological observations on satellite type and chromosome size suggest that the two Eurasian species B. benekenii (Lange) Trimen and B. ramosus Huds. are more closely related to the American species (B. ciliatus L., B. latiglumis Hitchc., B. pacificus Shear, and B. richardsonii Link) than to other Eurasian species. It is suggested that the section Pnigma may contain two distinct groups of species that can be separated on the basis of chromosome size.

Heterochromatin staining along with chromosome morphology was used to identify the chromosomes of Secale montanum Guss. in five accessions. The characteristics of all seven S. montanum chromosomes were fairly consistent from accession to accession. The S. montanum chromosomes were easily identified, and could be distinguished from the seven S. cereale L. chromosomes. Four disomic addition lines of S. montanum accession 2D23 to 'Kharkov M.C. 22' wheat were also analysed and identified.

Meiosis and chromosome morphology in females of a bivalent forming race of Mesocyclops edax (S. A. Forbes) are described. Meiosis is achiasmate and exhibits regular bivalent formation (2n = 14). Chromosome analyses of other populations of M. edax revealed that the females are heterozygous for several interchanges leading to the formation of large rings. Chromatin diminution during cleavage stages suggests that the elimination of H-segments occurs at the fourth cleavage division.

A set of seven primary trisomics and seven derived types were produced in Avena strigosa Schreb., a diploid oat species. Each trisomic type had a distinct phenotype. The primary trisomics were identified on the basis of plant and chromosome morphology. Although fertility (seed-set) and the frequency of transmission of the extra chromosome varied among selfed progenies of the various trisomics, each trisomic can be maintained. The trisomics occurred at a higher frequency in small seed fractions than in samples of large seeds. No straightforward relationship was apparent between chromosome length and trivalent formation but some association between trivalent formation and transmission rate was observed.Several qualitative and quantitative traits were compared between the primary telotri-somics, between these and the disomic and between opposite arm telotrisomics and their corresponding primary trisomic. It was concluded that the results are more compatible with dosage effects than with the gene balance theory.

The mitotic chromosome morphology and the meiotic chromosome behavior of Avena hybrida Peterm. are described for the first time. The haploid idiogram could be separated into four groups, the chromosomes within each being morphologically similar. There are three SAT-chromosomes (arm ratio (r) = 1.74-2.92), four metacentric chromosomes (r = 1.07-1.14), seven submetacentric chromosomes (r = 1.22-1.68) and seven subtelocentric chromosomes (r = 1.75-2.42). The idiogram of A. hybrida was compared with those of A. sativa cvs. 'Condor' and 'Markton'. Three chromosomes of 'Condor' differed significantly from those of A. hybrida, whereas no differences were apparent between the karyotypes of A. hybrida and A. sativa cv. 'Markton'. At meiosts 21 bivalents were regularly formed.

A procedure for chromosome banding in triticale has been shown to be equally effective on maize, Zea mays L., root tip chromosomes. Stocks of known knob constitution were used to demonstrate that differentially stained regions of C-banded mitotic chromosomes corresponded with knobs. The large knob and prominent chromomeres of abnormal chromosome 10 were also differentiated, as was the centric heterochromatin of B chromosomes. However, the large distal heterochromatic portion of the B was not differentiated by the procedure.

Datura stramonium L. (Solanaceae) is an annual weed found in most temperate and subtropical regions of the world. It has been recorded from all the provinces of Canada except Newfoundland, but is most common in Ontario and Quebec. It occurs in waste places, gardens, barnyards and, increasingly, in cultivated fields. Datura stramonium serves as an alternate host for many insect pests and diseases of Solanaceous crops, such as tomatoes, tobacco and potatoes, and has both narcotic and medicinal properties due to its production of a variety of alkaloids. It has been used extensively as an experimental plant in studies of genetics, chromosome morphology and embryonic development.Key words: Weed biology, jimsonweed, Datura stramonium, distribution

Cytological studies were made on the following taxa: C. addisonii, C. filifera, C. glaucophylla, C. pitcheri, C. reticulata, C. texensis, C. versicolor, and C. viorna. All species were found to have a somatic chromosome number of 16 with a uniform karyotype consisting of five pairs of metacentric chromosomes with centromeres in the median region and three pairs of acrocentric chromosomes, two pairs with centromeres in the terminal region and one pair with centromeres in the subterminal region. These findings agree with reports of chromosome number and karyotype for other species of Clematis and suggest a marked stability of chromosome complement in the genus.

The chromosomes of the Avena species were studied and their karyotypes established. The karyotype of the diploid species (excluding A. longiglumis) is designated as A. Longiglumis has a different karyotype with at least three chromosomes that have major changes. This karyotype is a modified A, designated as A′. The designation of the tetraploid karyotype is AB, including the basic set of chromosomes A and a second completely different set B. In the hexaploid species the basic set A is present but the B set is not; therefore the proposed designation is ACD. These results indicate an alloploid origin for the polyploid species.

Karyotypes of three eastern North American taxa of Actaea were investigated. Their karyotypes are as follows:[Formula: see text][Formula: see text][Formula: see text]Actaea rubra and its albino f. neglecta have identical karyotypes. The karyotypes of A. rubra f. rubra and A. pachypoda, two very distinct species, though similar, are clearly differentiated by the presence of a secondary constriction at the distal end of the long arm in the shorter of the two pairs of J-shaped chromosomes of A. pachypoda. The karyology of the three North American taxa is somewhat different from that reported by Kurita for A. asiatica.

Chromosome measurements including relative total length, arm ratio and centromeric index of the human complement were presented. Based on these data the human complement was classified into metacentric, submetacentric, subtelocentric, and acrocentric chromosomes and arranged into a mammalian style karyotype. On the basis of this classification a new karyotype was suggested to facilitate analysis of Denver Group III (X—6—12) and divide it into four subunits. Metacentric chromosomes 10 and 16 were detached from their respective groups in this new karyotype.

The morphology of the chromosomes of 16 Hordeum species was studied in considerable detail. No obvious trend in evolution is apparent from a study of the karyotypes of the species nor are any definite relationships with common barley (H. vulgare) indicated, except for two species, usually considered as being related, H. spontaneum and H. agriocrithon. On the basis of similarities of karyotype and morphological features of the plants seven groups were formed in which relationships are evident. The groups are: vulgare, marinum, murinum, californicum, stenostachys-pusillum, bulbosum, and jubatum. The plants within each group are identified by assigned numbers and by the specific names under which they were received. Within these groups are chromosome numbers of 14 and 28 and in one case 28 and 42. Allopolyploidy is indicated for most groups but H. bulbosum exists both as a diploid and as an autotetraploid.

An analysis was made of chromosome morphology and, by Feulgen cytophotometric measurements, of the nuclear deoxyribonucleic acid (DNA) content of L. corniculatus and related diploid species of the L. corniculatus group (L. alpinus, L. borbasii, L. corniculatus var. brachyodon, L. filicaulis, L. japonicus, L. krylovii, L. pedunculatus, L. schoelleri, L. tenuis) and L. coimbrensis of the L. aegeus group. The idiogram of L. coimbrensis differed markedly from those for the species of the L. corniculatus group, which were considerably more uniform. Lotus pedunculatus was the only species with chromosomes bearing satellites. Since L. corniculatus has a somatic chromosome number of 24, compared to L. corniculatus var. brachyodon with 12, the latter represents a new diploid taxon which should receive further taxonomic study. DNA values differed between the species, and in general, total complement lengths were correlated with DNA values. It is suggested that classical karyotype analysis may not be a suitable method to investigate the parentage of the tetraploid, L. corniculatus, because of chromosomal repatterning which has occurred during the evolutionary development of the closely related diploid species.

To establish a series of trisomics in Pennisetum typhoides (2n = 14), plants with 2n + 1 chromosome numbers were isolated from the progenies of triploid plants and triploid-diploid crosses. These primary simple trisomic plants were distinguishable from the diploids by their relatively poor vigour, short height, narrow leaves and late flowering. They were also distinguishable from one another and were classified into seven morphological groups: 'Tiny', 'Dark Green', 'Lax', 'Slender', 'Spindle', 'Broad' and 'Pseudonormal'. The extra chromosome in the seven trisomic types could be distinguished on the basis of somatic chromosome morphology.

Chromosome morphology, cell cycle dynamics and in vitro karyotype evolution are described for two heteroploid cell lines. For the male muntjac line, karyotypic changes are not correlated with gross shifts in the cell cycle.

The history and the present state of the classification of the Gramineae are briefly reviewed and a number of the different characteristics on which phylogenetic systems have been based are considered. The subjects of chromosome morphology and the application of idiograms and karyotypes to taxonomic studies are discussed. Avdulov's recently reported findings on the phylogeny of the grasses are summarized and compared with the results of other workers and those obtained in the present investigation. Three species of bamboos were studied for the first time and evidence secured to indicate that the basic number of the tribe is probably not 12 as has been elsewhere reported. In the Festuceae the chromosome number of Phragmites communis Trin. was definitely ascertained, confirming Avdulov's supposition that the basic number for the genus is 12. The other three species investigated agreed with the arrangement as proposed by Avdulov. The tribe Chlorideae, with the exception of the genus Beckmannia, has been reported to be almost entirely Panicoid with respect to chromosome morphology. This was confirmed in the four species examined. Avdulov's rearrangement of the tribe Hordeae was somewhat altered and a confusion m the nomenclature of the genus Lepturus was corrected. An anomalous situation was cleared up in the tribe Agrostideae by the establishment of the chromosome number of Sporobolus tennuissinus Kuntz as 40. The specimen of Anthoxanthum odoratum L. (tribe Phalarideae) examined provided a very interesting example of secondary splitting in somatic chromosomes. One species was examined in the tribe Melinideae and six in the tribe Paniceae. In the latter tribe no difference could be detected between the several subdivisions of the genus Panicum. The same condition held for the large genus Andropogon in the tribe Andropogoneae. In the tribe Maydeae the chromosome number of Tripsacum dactyloides L. was found to be 9, and the suggestion was made that it may be a link, along with the genus Coix, between the Andropogoneae and the Maydeae. The other four species examined all had a basic number of 10.

Chromosome morphology has been described in 20 species of Anemone s. lat. (Anemone s. str. 15 species, Pulsatilla 3, Hepatica 2). Two series, one based on 8 chromosomes and the other on 7, are present, in each of which two patterns can be recognized when an orderly arrangement of the chromosomes has been made. In the 8-chromosome series, the distinctions are based on differences in the arm ratio of chromosome IV, namely ratios of about 1:2 versus 1:1.4–1.8. Species in the first group include A. palmata, 2n = 16; A. parviflora, 2n = 16; A. caroliniana, 2n = 16; A. silvestris, 2n = 16; A. virginiana–riparia–cylindrica complex, (all 2n = 16); A. quinquefolia, 2n = 32; and species in the second group are A. pavonina, 2n = 16; A. coronaria, 2n = 16; A. hupehensis, 2n = 16; A. rivularis, 2n = 16; A. rupicola, 2n = 16; Pulsatilla pratensis, 2n = 16; P. nuttalliana ssp., 2n = 16; and P. occidentalis, 2n = 16. A. multifida, 2n = 32, has one chromosome set in each of the above groups. The 7-chromosome series falls into two groups on the basis of a combination of characters. Group one: long arms of chromosome I shorter than those of the longest chromosomes, long arms of chromosome II longer than those of the third pair, and arm ratios in chromosome II of 1.4–1.6. Group two: long arms of chromosome I longer than those of all others, long arms of chromosome II shorter than any of the others, arm ratios in chromosome II

Introduction The 21 illonosomic strains of the hard red spring wheat variety, Chinese Spring (Sears 1954), have been used to develop similar strains in other varieties. The monosomic condition is transferred to a variety by initial crosses between each of the 2 1 Chinese S ~ r i n e illonosomics and the reci~ient varietv. followed L U I J ' by a series of baclccrosses to recover the genotype of the recipient variety. In developing and maintaining monosomic strains, specific chromosomes are transmitted as univalents through successive generations. Since only a few chromosomes are ltnown to ~ r o d u c e ~ h e n o t v ~ i c effects in the monosomic state. infor1 I J 1 illation concerning chromosome morphology in different varieties is needed in ~. . . identifying monoson~ics. Sasalti et nl. (1963) have presented the lengths and characteristics of inetaphase I monosomes in the hard red winter variety, Cheyenne. Similar inforhation will be reported in this paper for another winter 6ariety, Wichita, using observations at metaphase I and anaphase 11. Throughout this study emphasis was placed on factors involved in sampling and measurement which might contribute to variations in chromoson~e length. Materials and Methods The inonosomic strains for the 21 different chromoso~nes of the hard red winter variety, Wichita C.I. 11952, were used in the present study. These strains had been derived by crossing Wichita as the male parent with each of the 21 inonosomic strains of Chinese Spring developed by Dr. E. R. Sears. Repeated baclccrossing of the derived monosomic plants to Wichita followed. At the time of this study five or six bacltcrosses had been con~pleted for all the chromosomes except 3B and jD, which had been bacltcrossed twice. Seeds of the monosomic strains were planted in 7-inch pots of soil in November, 1960, and the plants were grown in a plastic greenhouse. Artificial lights were provided during the flowering period. Following a vernalization period, the day temperature was controlled at 65" to 75°F. when the outside temperature was lower, and the night temperature at 50" to 55°F. Ample water and fertilizer were applied. Based on the findings of Sasalti et nl. (1963), a satisfactory method of sampling for statistical efficiency was found to include two monosomic plants for each chron~osome, four heads per plant, two slides per head, and two measurements per slide. In order to separate the date-of-sampling effects from head effects, an effort was made to collect saillples on two different dates from the same plant. taltine two heads on each date. I ' U Thus, for each sampling period, the aim was to obtain 16 measurements for each lcind of monosome, or a total of 336 measurements for the 21 monosonles. This was most nearly achieved for the metaphase I stage at the first

The chromosome complement in six turf-type genotypes of Poa trivialis was studied. The chromosome number was 2n = 2x = 14. On the basis of chromosome length, ratio between arm lengths, centromeric indices, and presence of constrictions all seven pairs were identified and characterized.