Cells of the connective tissue differentiate and migrate into pollen sacs

In angiosperms, archesporial cells in the anther primordium undergo meiosis to form haploid pollen, the sole occupants of anther sacs. Anther sacs are held together by a matrix of parenchyma cells, the connective tissue. Cells of the connective tissue are not known to differentiate. We report the differentiation of parenchyma cells in the connective tissue of two Gordonia species into pollen-like structures (described as pseudopollen), which migrate into the anther sacs before dehiscence. Pollen and pseudopollen were distinguishable by morphology and staining. Pollen were tricolpate to spherical while pseudopollen were less rigid and transparent with a ribbed surface. Both types were different in size, shape, staining and surface architecture. The ratio of the number of pseudopollen to pollen was 1:3. During ontogeny in the connective tissue, neither cell division nor tetrad formation was observed and hence pseudopollen were presumed to be diploid. Only normal pollen germinated on a germination medium. Fixed preparations in time seemed to indicate that pseudopollen migrate from the connective tissue into the anther sac.     

Fetal cystic hygromata: Insights gained from fetal blood sampling

Twelve second-trimester fetuses with cystic hygroma underwent fetal blood sampling for rapid karyotyping, haematologic evaluation, and blood gas analysis. An abnormal karyotype was found in seven cases: monosomy X in five, trisomy 21 in one, and trisomy 13 in the other. Eight often fetuses undergoing blood gas analysis showed hypoxaemia, five of which were growth-retarded. Nine pregnancies were terminated. Of the remaining three, only one fetus survived the perinatal period.     

方轧件在椭圆孔型中轧制温度场的三维有限元分析

应用MARC/autoforge有限元软件对方轧件在椭圆孔型中的轧制温度场进行了热力耦合模拟.研究了模拟过程中的传热边界条件,分析了轧制前和轧制过程中轧件中温度场的分布和变化规律.模拟计算结果和实验结果的比较说明二者基本是相符的.     

Zur Biotransformation des 1-Äthinylcyclohexylallophanats-(1)

The Science of Nature -     

本溪市区环境空气质量现状及变化趋势

对本溪市的环境空气质量进行了监测分析，结果表明：本溪市环境空气中TSP超过国家环境空气质量二级标准，SO2、NOx、CO、降尘均符合二级标准。其中TSP、SO2、CO、降尘呈下降趋势，NOx变化不明显。     

海南琼北火山监测与研究

本文通过对海南琼北火山地区火山地质构造、地震活动背景分析，阐明了以马鞍岭——雷虎岭火山为代表的历史喷发形式、构造类型、岩浆流的范围以及流向，论述了琼北火山是一个较典型的城市火山，是一个处于休眠状态的具有喷发危险的火山，并通过国内外火山活动监测与分析方法的对比，确定海南琼北火山活动监测、应急措施与对策。