MACROCYSTS IN THE LIFE CYCLE OF THE DICTYOSTELIACEAE. II. GERMINATION OF THE MACROCYSTS

Macrocyst germination was demonstrated in the five species of the Dictyosteliaceae known to produce these structures. The morphological changes that occurred during germination appeared to be identical in all of the strains examined, showing the following stages: (1) swelling of the dark, contracted content of the dormant cysts, (2) gradual loss of color and reappearance of cells within what previously appeared as a homogeneous protoplasmic mass, and (3) rupture of the heavy cellulosic cyst wall to liberate the myxamoebae. The age of the macrocyst appeared to be the most critical factor in determining whether or not germination would occur, since the cysts in many of the strains needed to age for several weeks or months before germination could be demonstrated. In Dictyostelium mucoroides strain DM-7, upon which the current study was centered, light was necessary to stimulate germination of young macrocysts—a requirement that gradually diminished as the cysts aged. The rate of germination and the temperature permitting germination were also age dependent: older macrocysts germinated more rapidly and at considerably higher temperatures than did young cysts. Although light was not essential for germination in every strain, the results obtained with strain DM-7 seem to be generally applicable to the germination process.     

MACROCYSTS IN THE LIFE CYCLE OF THE DICTYOSTELIACEAE. I. FORMATION OF THE MACROCYSTS

Macrocysts, a morphogenetic phase that is alternative to sorocarp formation in the life cycle of some cellular slime molds, are known for two genera and five species of the Dictyosteliaceae. In all of these macrocyst formation was found to be strongly affected by four factors: light, temperature, moisture, and the composition of the medium. In general, macrocyst formation was suppressed and sorocarp formation was enhanced by exposure to light, by incubation at temperatures lower than 20 C, by buffering nutrient media with phosphates, and by reducing atmospheric moisture through the use of clay covers on Petri dishes. The extent to which these environmental factors, singly or in combination, inhibited the production of macrocysts varied among the different strains and species.     

新疆甘草属的种间杂交

试验以居群为单位的新疆甘草属７个种进行种间人工杂交。通过对种间杂交结实量（ＲＳ）和亲本种平均结实量（ＲＳｍ和ＲＳｆ）的分析比较,测出相应的杂交结实指数（ＩＳ）、初步了解种间杂交亲和性的大小,为甘草属植物系统与演化的研究提供参考依据。     

INTERSPECIFIC HYBRIDITY IN THE DESMID GENUS PLEUROTAENIUM1

Three desmid taxa, isolated from different parts of Australia, conform to the morphological taxa Pleurotaenium ehrenbergii, P. mamillatum, and P. coronatum. Use of successful zygospore formation between cells of mixed populations as an indication of ability to share a common gene pool shows that all 3 taxa are at least closely related and probably are members of the same biological species. Tentatively, we suggest synonymy of these taxa and urge the adoption of sexual criterion in delimiting desmid species.     

INTERSPECIFIC CROSSES IN KALMIA

Interspecific crosses among Kalmia species are reported for the first time. All possible crosses between K. angustifolia, K. cuneata, K. latifolia, K. hirsuta, K. polifolia var. rosmarinifolia and K. p. var. microphylla were attempted. Several crosses yielded no hybrids, many produced albino or yellow-green inviable seedlings, and six combinations produced at least a few seedlings with near-normal growth habit. Stylar inhibition of pollen tube growth prevented some species from hybridizing; reciprocal differences in crossability and pollen tube growth were noted. Kalmia species are highly heterozygous, but no evidence was found within a species for geographic variation of combining ability except for the two varieties of K. polifolia which had different crossing patterns with the other species. The anthocyaninless form of K. angustifolia, in contrast to the normal, has unique combining ability with K. latifolia. No genetic evidence was found to support the placement of K. hirsuta in another genus (Kalmiella) or to designate K. angustifolia var. caroliniana as a distinct species. Use of all the species to breed improved ornamentals is limited by genetic barriers and sterility of F₁ hybrids.     

棉属种间高代系的过氧化物酶同工酶研究

利用薄层等电聚焦方法,对已稳定遗传２０代的棉属陆地棉（Ｇｏｓｓｙｐｉｕｍ ｈｉｒｓｕｔｕｍ ）×中棉（Ｇ．ａｒｂｏｒｅｕｍ ）种间高代系蕾期真叶及花药中的过氧化物酶同工酶进行研究,结果表明：１．同一棉种的不同品种,其过氧化物酶同工酶基本相同,同一染色体组的不同棉种,其过氧化物酶同工酶存在一定的差异,不同染色体组的棉种,其过氧化物酶同工酶存在显著的差异;２．高代系的同工酶谱与母本“科遗２号”相似,而与父本中棉“完紫”具有较大的差异     

INTERSPECIFIC TRANSFORMATION IN BACILLUS

Marmur, J. (Brandeis University, Waltham, Mass.), E. Seaman, and J. Levine. Interspecific transformation in Bacillus. J. Bacteriol. 85:461-467. 1963.-Deoxyribonucleic acids (DNA) from various species of the taxonomic group Bacillaceae were examined for base composition, ability to carry out interspecific transformation, and formation of molecular hybrids in vitro. The minimal requirement for genetic compatibility among different species and for DNA interaction (both reflecting base sequence homologies) is the similarity of the guanine plus cytosine contents of the DNA. The close correlation between the ability of DNA to be competent in interspecific transformation and to form hybrid molecules on denaturation and annealing provided a rational approach to the study of genetic relationship among organisms for which no genetic exchange has yet been demonstrated. Any or all of the criteria (base composition of DNA, transformation, molecular hybrid formation) can be used as tools in the taxonomic assessment of closely related microorganisms.     

ON THE NATURE OF INTRA- AND INTERSPECIFIC INCOMPATIBILITY IN ULMUS

Efforts to introduce Dutch Elm Disease resistance into the American elm (Ulmus americana L.) through breeding with Asian elms has been hampered by sexual incompatibility. Controlled pollinations of Ulmus americana and the Siberian elm (Ulmus pumila L.) were studied in detail to gain insight into the nature of this incompatibility. Microscopic observations revealed that germination and early pollen tube growth were inhibited on the stigmatic surface following both intra- and interspecific incompatible pollinations. Both qualitative and quantitative differences in pollen inhibition on the stigmatic surface indicated that the inhibition may involve the action of an inhibitory substance. Detailed observations on callose deposition indicated that this β-1,3 glucose polymer may implement the inhibition.     

长喙毛茛泽泻的种群分布格局和群落内种间关联

长喙毛茛泽泻茶陵种群呈斑块分布,格局类型为聚集分布型,每个亚种群也呈聚集分布,但聚集强度不同。长喙毛茛泽泻与其几个主要伴生种的相关性经测定结果是：与莼菜及黄花狸藻之间的相关性不显著;与柳叶箬、双穗雀稗及石龙尾之间正相关显著;与疏勿蓼之间负相关显著,长喙毛茛泽泻种子近距离传播以及无性繁殖特性是造成其聚集分布的主要原因。柳叶箬、双穗雀稗和石龙尾对长喙毛茛泽泻具有极强的竞争作用。     

INTERSPECIFIC INCOMPATIBILITY IN SOLANUM SPECIES

Pandey , K.K. (Crop Res. Div., D.S. & I.R., Lincoln, Christchurch, New Zealand.) Interspecific incompatibility in Solanum species. Amer. Jour. Bot. 49(8): 874–882. Illus. 1962.—A diallel cross involving 11 self-incompatible and 3 self-compatible species of Solanum was made to study the genetic basis of interspecific incompatibility. Interspecific incompatibility was not limited to crosses in which a self-compatible species was used as the male parent onto a self-incompatible species (unilateral incompatibility). A number of crosses between self-incompatible species were incompatible. In one cross, Q vernei X verrucosum, a self-compatible species was successful as a pollen parent with a self-incompatible species. Unlike other hybrids between self-compatible and self-incompatible species, which are self-incompatible, these F₁ hybrids were self-fertile, and cross-fertile among themselves and with both parents. The self-fertile S. polyadenium was cross-incompatible as a female as well as a male parent with all other species. It is suggested that the unilateral incompatibility is a property of the allele S_C which originated as a consequence of one kind of breakdown of the S_I gene; the S_C allele produces “bare” pollen growth substances which are inactivated in an incompatible style. It is proposed that the failure of the principle of unilateral interspecific incompatibility in solanaceous species may be due to the action of alleles at the second incompatibility locus revealed in certain Mexican species. It is assumed that the South American species are selected intraspecifically only for the action of S alleles but that in certain interspecific crosses and rarely in intraspecific crosses the alleles at the second locus may be expressed, thus interfering with the usual action of S alleles. The F₁ hybrids Q verrucosum (self-fertile) X simplicifolium (self-sterile) were self-incompatible at the tetraploid as well as the diploid level, and their cross-compatibility behavior was consistent with the expected activity of the S_C and S_I alleles of the 2 parents respectively.     

INTERSPECIFIC HYBRIDIZATION IN HAPLOPAPPUS AND ITS BEARING ON CHROMOSOME EVOLUTION IN THE BLEPHARODON SECTION

Jackson , R. C. (U. Kansas, Lawrence.) Interspecific hybridization in Haplopappus and its bearing on chromosome evolution in the Blepharodon section. Amer. Jour. Bot. 49 (2) : 119–132. Illus. 1962.—Cytological analyses of interspecific hybrids between H. gracilis (n = 2) and H. spinulosus ssp. australis (n = 8) indicate that ssp. australis is a segmental allotetraploid, derived from past hybridization between 2 taxa with chromosome numbers of n = 4. Analysis of hybrids between H. gracilis (n = 2) and H. ravenii (n = 4), a previously undescribed species, has shown that the chromosome segments of these 2 species are almost completely homologous. Differential contraction is suggested as the explanation for the disappearance in late pachytene of presumed non-homologous segments which were evident in some cells at early pachytene. The pairing relationship of gracilis and ravenii chromosomes at pachytene and later prophase I stages of meiosis indicates that gracilis has evolved from ravenii by an aneuploid reduction process similar to that described for Crepis. The close morphological relationship of the 2 species adds further support to this proposition. Data from the cytological analysis of both interspecific hybrids indicate that x = 4 is the basic chromosome number for the Blepharodon section of Haplopappus.     

INTERSPECIFIC COMPETITION ALTERS NONLINEAR SELECTION ON OFFSPRING SIZE IN THE FIELD

Offspring size is one of the most important life‐history traits with consequences for both the ecology and evolution of most organisms. Surprisingly, formal estimates of selection on offspring size are rare, and the degree to which selection (particularly nonlinear selection) varies among environments remains poorly explored. We estimate linear and nonlinear selection on offspring size, module size, and senescence rate for a sessile marine invertebrate in the field under three different intensities of interspecific competition. The intensity of competition strongly modified the strength and form of selection acting on offspring size. We found evidence for differences in nonlinear selection across the three environments. Our results suggest that the fitness returns of a given offspring size depend simultaneously on their environmental context, and on the context of other offspring traits. Offspring size effects can be more pervasive with regards to their influence on the fitness returns of other traits than previously recognized, and we suggest that the evolution of offspring size cannot be understood in isolation from other traits. Overall, variability in the form and strength of selection on offspring size in nature may reduce the efficacy of selection on offspring size and maintain variation in this trait.     

猕猴桃属种间体细胞杂种

利用PEG融合方法,分别进行了中华猕猴桃(Actinidia chinensis var.chinensis)(2n=2x=58)子叶愈伤组织来源的原生质体与美味猕猴桃(A.deliciosa var.deiciosa)(2n=6x=174)子叶愈伤组织原生质体、以及狗枣猕猴桃(A.kolomikta)(2n=2x=58)叶肉原生质体种间原生质体融合。结果表明:中华猕猴桃与美味猕猴桃融合的1个克隆和中华猕猴桃与狗枣猕猴桃融合的4个克隆的RAPD谱带分别具有双亲特异的DNA谱带;经流式细胞仪分析,前者细胞核倍性推测为8倍体,后者细胞核为3倍体、4倍体和5倍体。初步鉴定这5个克隆是猕猴桃属种间体细胞杂种。     

DICTYOSTELIUM AUREO-STIPES AND DICTYOSTELIUM TENUE: NEW SPECIES OF THE DICTYOSTELIACEAE

Three new cellular slime molds, Dictyostelium aureo-stipes sp. n., D. aureo-stipes var. helvetium var. n. and D. tenue sp. n., are described which possess characteristics heretofore unrecorded in the Dictyosteliaceae. The two species are unlike in dimensions and complexity of form, yet show a number of features in common, and may in fact be closely related. D. aureo-stipes var. helvetium is relatively large and robust, forming multiple-branched fruiting bodies without the regularity of form found in Polysphondylium, yet tending toward symmetry when well-developed. The golden-yellow stipe is a distinguishing feature of D. aureo-stipes and is even more pronounced in var. helvetium. D. tenue is smaller and simpler in form. The degree of branching is much reduced, and oftentimes a solitary sorus terminates a delicate stipe composed of a single tier of cells. Both species are quite sensitive to environmental conditions, particularly temperature, for optimum development occurs within relatively narrow ranges.