Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Contributions to the cytòtaxonomy of the Commelinaceae

Representatives of the Tradescantia geniculata alliance (genus Gibasis Rafin.) in cultivation at Kew display considerable cytological and morphological diversity. Chromosome complements consist of either large or small chromosomeS. Plants with small chromosomes have either 2 n = 16 or 2 n = 32, and all form only bivalents at meiosis and have presumed basic numbers of x – 8 and x = 8 or 16 respectively. The 2 n = 32 accessions are considered to represent T.geniculata in its strict sense; the identity of the 2 n =16 plant is uncertain. Plants with large chromosomes have either 2 n = 16 or 2n = 20 and each forms quadrivalents to the extent that they can be considered as cytological autotetraploidS. Basic numbers are then x = 4 and x =5, the lowest yet recorded for the Commelinaceae. The identity of the x = 4 species is uncertain. The x = 5 plants are readily identified as T.karwinskyana.     

Contributions to the Cytotaxonomy of the Commelinaceae. Gibasis linearis and its allies

Species of the Gibasis linearis alliance collected in Mexico in 1976 are shown to have a chromosome constitution of x = 6, but x = 5 has also been found in some populations of G. rhodantha and G. speciosa. These two basic numbers are associated with distinctive karyotypes, 2M + 4A and 3M + 2A respectively, which show a Robertsonian relationship with each other. The existence of 2n = 22 in G. speciosa , combining both basic numbers at the amphidiploid level provides evidence of pairing between metacentrics and acrocentrics in such a way as to substantiate the view that fusion or fission of chromosomes is responsible for the modification of basic number. This survey provides a basis for other studies which will determine the chromosome relationships of the species irrespective of chromosome number in this family.     

Contributions to the Cytotaxonomy of the Commelinaceae. Gibasis linearis and its allies

Species of the Gibasis linearis alliance collected in Mexico in 1976 are shown to have a chromosome constitution of x = 6, but x = 5 has also been found in some populations of G. rhodantha and G. speciosa. These two basic numbers are associated with distinctive karyotypes, 2M + 4A and 3M + 2A respectively, which show a Robertsonian relationship with each other. The existence of 2n = 22 in G. speciosa , combining both basic numbers at the amphidiploid level provides evidence of pairing between metacentrics and acrocentrics in such a way as to substantiate the view that fusion or fission of chromosomes is responsible for the modification of basic number. This survey provides a basis for other studies which will determine the chromosome relationships of the species irrespective of chromosome number in this family.     

Contribution to the cytotaxonomy of Oryzopsis (Poaceae)

Meiotic studies were performed in twelve populations of four Oryzopsis species (O. pubiflora, O. lateralis, O. holciformis var. longiglomis and O. barbellata) to obtain data on the ploidy level and cytological evolution of the genus. The chromosome number 2n=2x=24 was revealed in all the species and populations studied. The present and other studies show the occurrence of two basic chromosome numbers in the genus, i.e. x=11 and x=12. Although Oryzopsis species and populations studied are diploid and are expected to form only bivalents in metaphase of meiosis‐I, quadrivalents were observed in O. pubiflora and O. lateralis, possibly due to the occurrence of heterozygote translocations. B‐chromosomes of 0–2 were observed in all species and populations studied. This is the first report of the occurrence of B‐chromosomes in the genus Oryzopsis. Several meiocytes showed the presence of double chromosome number in O. lateralis, and multipolar cells were observed in populations of O. barbellata, O. lateralis and O. holciformis var. longiglomis. The occurrence of large pollen grains (possibly unreduced) was observed along with smaller (normal) pollen grains in these species. Significant differences observed in chiasma frequency and distribution among studied species may be of use in species delimitation. The Kakan population differed significantly from the other populations of O. lateralis in meiotic characteristics. If such cytological differences are accompanied by morphological variation (under investigation), we may consider this population as a new variety or subspecies.     

Ustilaginales of Commelinaceae

The seven reported smut fungi on Commelinaceae are revised. Of these, five are recognised and described:Ustilago aneilematis, U. burkillii, U. commelinae, U. nawaschinii andU. tinantiae. Entyloma commelinae is considered to be a doubtful species andU. rwandensis is a synonym ofU. aneilematis. A new species,Ustilago combensis (type onCommelina benghalensis) is proposed. A key to thesee species is presented.Studies in Heterobasidiomycetes, part 102     

Self-incompatibility in the Commelinaceae

This paper reports on a survey of self-incompatibility in 110species of 22 genera in the family Commelinaceae. Genera fromboth tribes, Tradescantieae and Commelineae are included. Fifty-fivespecies were found to be self-incompatible, 50 species self-compatible,and five species comprised individuals which were self-incompatibleand individuals which were self-compatible. This variabilityand its possible evolutionary significance are discussed. Self-incompatible species had actinomorphic flowers and themajority of these were in the Tradescantieae. Species with zygomorphicflowers which were more commonly found in the Commelineae wereself-compatible. The ubiquitous presence of binucleate pollengrains supports previous data that self-incompatibility is ofthe gametophytic type. The site of pollen tube arrest, however,was on the stigma at or near the base of the stigma papillacells. There were two exceptions to this viz. an unnamed Dichorisandraspecies and Siderasis fuscata where pollen tube arrest was stylar. The significance of these data to taxonomy also receives comment. Commelinaceae, incompatibility, self-compatibility     

Flavonoids and chemotaxonomy of the Commelinaceae

Diverse schemes have been proposed for the classification of the Commelinaceae on the basis of different characters. The leaf flavonoids of 152 species have been analysed. The flavone C-glycosides are the dominant compounds, found in 78% of the species examined. Flavonol O-glycosides are present in 28% of the species, quercetin being the most frequent aglycone. 6-Hydroxyluteolin was found mainly in Tradescantia but also in other species (10%). Tricin has been detected sporadically in less than 5% of the species. In spite of these variations the pattern of the family is very uniform, because the presence of C-glycoflavones and the distribution of the other compounds supports the scheme proposed by Rohweder who divided the family into Commelinieae and Tradescantieae on the basis of inflorescence characters.     

On the cytotaxonomy of phasmids (Phasmatodea)

Summary A wide diversity in chromosome complement is found in two species of phasmids of the primitive group Prisopini—Prisopus ariadne Hebard and Prisopus berosus Westwood. P. ariadne has a diploid male complement of 28, comprising 13 pairs of relatively large mediokinetic autosomes and Neo XY sex chromosomes. P. berosus, 2n =49, has relatively small autosomes most of which are mediokinetic, and retains the XO—XX sex mechanism. Chromosomal polymorphism in this species is suggested by the presence of an unequal pair of autosomes and a structural differentiation in the X in one of two males studied.The relative amount of DNA per nucleus in male germ cells (Peulgen cytophotometry) shows a significant difference in total chromosomal content between the complements of the two species.These data are discussed with reference to the cytotaxonomy of phasmids.Supported in part by research grant G-4370 from the National Institutes of Health, Public Health Service.     

核型分析在细胞分类学中的应用

细胞学的核型分析资料作为分类学的证据,结合形态学、解剖学、胚胎学和遗传学等方面的证据,在解决分类上的疑难问题,起过不少的作用,而且是建立生物学种和建立新的自然分类系统所必不可少的资料。     

Giemsa C-banding of Rhoeo (Commelinaceae)

The C-banded karyotypes of the three known varieties of Rhoeo are presented for the first time. Each variety displayed the same banding pattern with C-bands identified at all centromeres and some telomeres. In addition, the karyotype of a rare bivalent-forming Rhoeo was ascertained to consist of two complexes using C-banding. The nature and location of Rhoeo's C-bands are discussed.This paper represents part of a dissertation submitted for a Ph.D. thesis at West Virginia University.     

我国直翅目昆虫细胞分类学研究现状

从研究材料、研究方法、染色体研究在昆虫分类上的应用 3个方面对我国昆虫尤其是直翅目昆虫的细胞分类学研究情况作了简要的概述 ,并着重论述了直翅目昆虫的核型及带型的研究现状 ,同时对我国直翅目昆虫分类学的发展前景进行了展望     

Contributions to the Biomechanics of Plants.; II. Stability Against Local Buckling in Hollow Plant Stems*

Hollow plant stems are, compared to solid ones, endangered by a particular kind of mechanical damage: local buckling. In upright stems centric forces due to the weight of the plant itself are not critical. Bending, however, as caused by wind forces causes transverse stresses that lead to local buckling, long before the critical tension or compression stresses are reached. A new numerical method is proposed to treat local buckling of hollow plant stems caused by bending forces. The results emphasize the importance of transverse reinforcements in the nodes and/or the nodal thickenings for the stability of hollow structures.