VARIATIONS WITHIN SINGLE CELL CLONES OF TOBACCO TISSUE CULTURES

Comparative studies were made utilizing two series of secondary clones (single cell clones derived from single cell clones H 196 and H 241) of hybrid tobacco (Nicotiana tabacum ♂ × Nicotiana glutinosa ♀ ) tissue grown in vitro. Secondary clones derived from a single parent varied in color, consistency, the ability to grow, and rate of growth with various carbohydrates and growth-promoting substances. The growth of the secondary clones generally resembled that of the parent clone from which derived. Many of the 23 secondary clones of H 196 grew satisfactorily on media supplemented with sucrose, dextrose, levulose, or maltose; lactose, galactose, and xylose were unsatisfactory supplements. Similarly, the series of 30 secondary clones isolated from H 241 grew well on some media but poorly on others. Growth generally decreased when α-napthaleneacetic acid or 2,4-dichlorophenoxyacetic acid was omitted from the basal coconut milk medium. Growth decreased considerably when coconut milk was omitted from the basal medium. The optimum sugar concentration was 1/2 to 1 per cent.     

金沙江干热河谷种子植物区系特征的初探

研究涉及金沙江云南境内的干热河谷和干暖河谷的种子植物区系。建立名录共920种,有野生植物748种。这748种,分属于111科,427属。427属的分布区类型的格局为：l－44,2—127,3—10,4—39,5—13,6—37,7—29,8—47,9—12,10—25,11—3,12—7,13—l,14—20,15—13．在748种中,三江（金沙江、元江、怒江）干热河谷共有的标志植物73种,金沙江的标志植物156种,它们是研究区系特征的基础。经分析,本区植物区系有以下特征：(1)属、种均以热带成分为主,热带属占66.58%,种的热带成分更多,均交错少数温带成分;(2)三江干热河谷共同标志植物中,多数是优势种或常见种,例如Heteropogon contortus, Bombax ceiba,Phyllanthus emblica,Euphorbia royleana,Tribulus terrestris等,地区特有成分则少,如Terminalia franchetii,Andropogon yunnanensis;(3)滇北、川西南河谷特有成分则较多,如Cycas panzhihuaensis,Nouelia insignis,Aristolochia delavayi等;(4)西南特有成分也较多,且在河谷常见,如Delavaya yunnanensis,Croton yunnanensis,Munronia delavayi等;(5)有一些非特有的特殊种类,如Heteropogon melanocarpus,Dinebra retroflexa等.鉴于特征分析,本区植物区系有以下几个更深层的特征:(1)热带起源与近代交错现象;(2)有古地中海区系的后裔;(3)与近代非洲与南亚区系有联系;(4)与华北区系有联系;(5)特有现象明显而成因复杂,等。     

CHROMOSOME NUMBERS IN BROMELIACEAE

Eighty-three chromosome counts are reported for 72 taxa of the Bromeliaceae. Fifty-eight of these counts are the first known chromosome number reports for their respective taxa. A model of chromosomal evolution in the Bromeliaceae (n = 25) is presented. The model is parsimonious and consistent with existing data on meiotic chromosome numbers within the family and in the closely related Velloziaceae (n = 9). Two hypothesized paleodiploids (n = 8 and n = 9) hybridized to form a tetraploid that in turn hybridized with the n = 8 lineage. The resultant n = 25 is the extant base number for the family. Two alternative hypotheses could explain the unique extant base number (n = 17) for Cryptanthus: 1) Cryptanthus represents the paleotetraploid level, i.e., prior to the second round of hybridization, or 2) the lower number represents the result of a more recent series of aneuploid reductions from n = 25. Given the existence of intergeneric hybrids involving Cryptanthus, aneuploid reduction is the more likely interpretation.     

CHROMOSOME NUMBERS IN WESTERN GRASSES

Chromosome numbers are reported for 221 collections from eleven western states. These records represent 85 species included in 48 genera. Counts for the following species are here presented for the first time: Melica spectabilis, Blepharidachne kingii, Eragrostis obtusijlora, Hilaria rigida, Redfieldia flexuosa, and Sporobolus interruptus. The record for Redfieldia is also the first for that genus. In addition, numbers which differ from those in the literature are recorded for ten species, in three cases two different numbers for the same taxon. Cytological evidence is also presented indicating that Hilaria jamesii and H. rigida have hybridized and that the F₁ has backcrossed to both parents.     

CHROMOSOME NUMBERS IN MEXICAN ASTERACEAE

Chromosome numbers are reported for 100 collections distributed among 68 species and 46 genera of Mexican Asteraceae. Included are systematic discussions regarding chromosome numbers of the following taxa: Haplopappus spinulosus var. scabrellus (n = 4, 8); Hofmeisteria fasciculata (n = 19), Malperia tenuis (n = 10), and Pleurocoronis laphamioides (n = 9); Cymophora pringlei (2n = 16); Plummera (n = 15); and Porophyllum tridentatum var. crassifolium (n = 15) as related to Chrysactinia and Nicolletia.     

CHROMOSOME NUMBERS OF SOME SACCHARUM SPECIES HYBRIDS AND THEIR CELL SUSPENSION CULTURES

Chromosome numbers of five Saccharum species hybrids and their cell suspension cultures were determined. The chromosome number was stable in four parental clones (2n = 122, 114, 114, and 112), but was variable in another (2n = 108-128). The cell suspension cultures have been maintained in a yeast extract-enriched nutrient medium for more than 6 years. These cultures were variable in chromosome number for all clones, with a partial aneuploid series at the haploid and/or polyploid level. Each clone had different chromosomal population modes after 6 years of culture. The loss of chromosomes over a period of time would have an effect on the genetic makeup of a cell population. This has implications in the use and interpretation of data from pathological, cytogenetical, biochemical, and physiological studies using cell cultures and is probably a partial explanation for the loss of totipotency in 6-year-old sugarcane tissue and suspension cultures.     

SOME CHROMOSOME NUMBERS OF DRAPARNALDIA

The variability exhibited by Draparnaldia both in nature and in the laboratory makes it difficult to identify the species. The natural variability of Draparnaldia was amplified by the environmental conditions and the media used in this study. With the hope that chromosome studies would aid in taxonomic characterization by providing additional differentiating criteria, special attention was devoted to adapting techniques which could be used to determine chromosome numbers of Draparnaldia isolates. The chromosome numbers reported herein are as follows: (1) Draparnaldia glomerata, Isolate #1, isolated from Davis Falls, Montevallo, Alabama, was found to have a chromosome number of 13. (2) Draparnaldia Isolate #2, an unidentified species obtained from Anniston, Alabama, was found to have a chromosome number of 13. (3) Draparnaldia acuta, Isolate #3 from Northwood Lake, Northport, Alabama, exhibited 26 chromosomes. (4) Draparnaldia plumosa strain 423 (Indiana Culture Collection), 418/a (Cambridge) was observed to have a chromosome number of 13.     

中国苹果属植物染色体数目报告

本文观察了中国苹果属植物17个种22个材料的染色体数目。观察结果指出,多倍体在全部研究材料中占44.6%,其中有些种因材料来源不同,其倍数性各异。本结果可供我国苹果遗传育种参考。     

CHROMOSOME NUMBERS IN PURE AND GROSS CULTURES OF MYXOMYCETES

Certain strains of Myxomycetes grown in pure culture in liquid media display widely varying chromosome numbers which indicate the presence of polyploid series of amoebae and plasmodia. The implications of these chromosome number variations on existing controversies concerning Myxomycete life cycles and cytology are discussed.     

RATES OF EVOLUTIONARY CHANGE IN CHROMOSOME NUMBERS IN SNAILS AND VERTEBRATES

Mollusks and most non-mammalian vertebrates have been characterized as evolving an order of magnitude more slowly in morphology and karyotype compared with most groups of placental mammals. New calculations of the previously used measures of chromosomal rates of evolution for different groups of gastropods, using a larger and taxonomically broader sample, indicate that these rates had been previously underestimated, although they are still lower than those of the most rapidly evolving placental groups. When genera of approximately the same geological age are compared, little difference (less than an order of magnitude) in fossil-based measures of average rate of karyotypic evolution are found among placental mammals, frogs, lizards, and snails. Variation in rates within major groups obtained from the limited available data does not allow clear generalizations on among-group differences in chromosomal rates of evolution.     

CHROMOSOME NUMBERS IN CHEILANTHES AND POLYPODIUM

Six chromosome observations are reported, two being confirmations and four being new counts. Polypodium plesiosorum (from Mexico) shows 37 pairs at meiotic metaphase and thus conforms to past counts of diploid species in this genus. Cheilanthes wrightii (Arizona) has 2n = 58 and is a diploid member of the x = 29 series of that genus. Cheilanthes tomentosa (Alabama) shows 90 units at metaphase of meiosis and approximately the same number during mitosis in the crozier cells. It has 32 spores and our plant is an apogamous triploid. Both Cheilanthes siliquosa (Washington) and C. californica (California) show 30 pairs at meiotic metaphase. Counts on plants identified as C. carlotta-halliae (California) show 30 bivalents and 30 univalents at diakinesis, suggesting that they actually represent allopolyploid backcrosses of C. carlotta-halliae and one of its parents.     

CHROMOSOME NUMBERS IN THE GENUS ANTHURIUM

Chromosome numbers were determined for 63 Anthurium species. Thirty-eight of these were newly determined. Generally the present work confirmed existing chromosome counts when these were available for comparison. The most common somatic chromosome number found was 30, but counts ranged from 2n = 20 to 90. In a few instances conflicting counts were obtained. B chromosomes were found frequently in Sect. Cardiolonchium and varied in number from one to three. Four polyploid series were evident from all available counts: 20-40, 24-30-48-84, 28-56 and 30-60-90-ca 124. Most species were part of the polyploid complex based on 30. Although species were not observed with n = 5, 6 or 7, movement among the basic numbers was considered to have occurred at this level. The relationship among these basic numbers and n = 15 (x₂) is still obscure.