THE INFLUENCE OF PRESSURE ON THE DIFFERENTIATION OF SECONDARY TISSUES

Brown, Claud L. (U. Georgia, Athens), and Karl Sax. The influence of pressure on the differentiation of secondary tissues. Amer. Jour. Bot. 49(7): 683–691. Illus. 1962.—When longitudinal bark strips of Populus trichocarpa and Pinus strobus are separated from the bole wood during early spring and maintained in a humid environment while attached to the parent tree, the cambial zone along the inner surface of the segments rapidly proliferates producing an extensive parenchymatous callus. Subsequently, a new phellogen and cambium differentiate and extend tangentially around the outer periphery of the callus pad, this resulting in the formation of a new stem-like structure. Whenever bark strips are separated from the bole wood by a layer of polyethylene plastic film and held firmly against the tree by externally applied pressure, the cambium continues to function normally, setting aside derivatives which differentiate and mature into normal, elongate xylary and phloic elements. The importance of mutual pressures and spatial relationships in controlling patterns of differentiation in secondary tissues is clearly demonstrated.     

地形对森林群落年龄及其空间格局的影响

 地形已被广泛认为是植被环境时空异质性的重要来源,但其对山地森林群落动态的影响及其机理仍不清楚。作者在三峡大老岭选取一块200 m×100 m的常绿落叶阔叶林样地, 在样地植物群落调查的同时,建立了1∶500的数字高程模型,并利用树木年轮数据和分种的胸径 年龄幂函数模型,推算了全部10 m×10 m单元样方的群落年龄。统计了样地群落的年龄结构及其代表种的构成特征,并利用多元回归结合方差分析方法分析了地形和生物因子对群落年龄结构的影响与途径。结果表明：1）幂函数模型很好地拟合了16个树种的胸径-年龄数量关系;2）样地内群落斑块的年龄介于14～179年,平均值在95年左右;3）代表样方群落年龄的树种共有24 个,而前5种即在68.5%的样方中决定群落的年龄;4）回归分析表明群落年龄受到溪流影响指数、坡位、坡度、样方内受干扰木胸面积和树种生长指数等因素的显著影响。显示沟谷地 表径流冲击和表土侵蚀等坡面过程带来的干扰明显影响群落发育过程的空间格局,具有不同生态习性树种的潜在年龄也限制了群落的现实年龄;5）地形主要通过控制地表干扰体系的时空分布和不同物种的选择性分布两方面而对群落动态与年龄产生影响。但由于生态格局自身的复杂性与随机性和分析方法带来的误差,使基于地形的群落年龄格局预测结果还存在较大的不确定性。     

地形对亚热带山地景观尺度植被格局影响的梯度分析

用 7个指标反映三峡大老岭地区森林群落生境的地形特征 ,采用 DCCA排序方法定量分析不同地形因子对亚热带山地森林植被格局的影响及它们各自的生态意义 ;并分析它们的作用强度沿海拔的变化。结果表明 :1)DCCA排序的前 4个轴分别与海拔、坡位和坡度、坡向和坡面显著相关 ;山地森林植被存在多重尺度和方向的分异格局 ;2 )山地森林群落样方生境的热量、水分 (养分 )和光照条件可主要由海拔、坡位和坡度、坡向等地形特征分别反映 ;3)在垂直梯度上 :海拔的影响在海拔 6 0 0～ 80 0 m和 15 0 0～ 170 0 m最大 ;坡向影响的峰值在山顶带 ;坡度、坡位与坡形的影响在山地中部影响最大 ,其中坡度在海拔 6 0 0 m以下的影响也很显著 ;坡面的影响在山地中部最显著。     

甲基胆蒽对蝾螈中胚层分化的影响

前言对哺乳类有引瘤作用的物质,在两栖类的成体中,不论是有尾类(Breedis,1951,1952;和,1954)或者无尾类(曾弥白,1956a),都可以引起恶性瘤肿,虽然瘤肿形成的频率远没有在哺乳类高。对于两栖类幼体,或者正在发育中的胚胎组织,引瘤物质却表现了不同的作用。它们可以引起形态建成的变化。Waddington 和 Needham(1935)将多种多环碳氢化物塞入早期原肠胚的囊胚腔,发现其中几种诱导了神经组织的发生。为了避免塞入法可能引起的机械的影响,沈诗章(Shen,1942)用二苯骈蒽内琥珀酸钠(Na-dibenz-anthracene-endo-succinate)的水溶液处理早期原肠胚的预定表皮,也得到了同样     

不同的基质表面形貌对细胞生长行为的影响

在细胞体外培养中,基质的表面形貌特征是影响细胞行为的一个重要因素。在微米尺度范围内本文研究了几种不同几何轮廓的脊／沟状形貌结构和不同间距的柱状体对鼠C6神经胶质瘤细胞生长的影响。脊／沟状形貌结构诱导细胞趋向生长,不同的几何轮廓对细胞行为的影响存在差异。柱状体间距影响细胞的贴壁和铺展,进而影响细胞的生长行为;大的间距不利于细胞生长,当间距很小时,柱状体截面的几何轮廓影响细胞的行为。     

THE INFLUENCE OF SPECIMEN TOPOGRAPHY ON X-RAY MICROANALYSIS ELEMENT MAPPING

The effect of specimen topography on x-ray microanalysis element mapping was studied with an electron microprobe and a scanning electron microscope equipped for x-ray detection. Using the lemma and palea of rice inflorescences as models, we determined that specimen topography can physically limit the detection of x-rays and thus lead to erroneous element mapping data. Any geometrical point on a specimen interfering with a straight line from the point of excitation to the detector will cause an absorptive shadow area on the element map. Electrons impinging on a sample surface cause emissions to occur in all directions. Emissions with sufficient energy (x-rays and backscattered electrons) can strike a topographical point different from the location of the focused electron beam, causing detectable x-ray excitation. This phenomenon will also result in erroneous element map data. Methods of recognition of specimen topographical effects on x-ray microanalysis are discussed.     

A NOTE ON THE UNUSUAL CRUSTACEAN COMMUNITY OF A TEMPORARY POOL IN THE NORTHERN CAPE

Summary

A temporary pool in a dry stream bed traversing Grootvloer Pan in the Northern Cape was inhabited by fifteen branchiopod and calanoid copepod crustacean species. There was an unusually high number of congeneric species in the pool; in the class Branchiopoda, five Streptocephalus species and four Daphnia species were collected. In addition, two species of the calanoid genus Metadiaptomus were identified. The high species richness was not related to habitat diversity, pool size or difference in body size of each species. Three species (Streptocephalus purcelli, S. gracilis and Metadiaptomus capensis) had previously been collected only from the winter-rainfall areas of the Cape. Episodic flooding in the Northern Cape in 1988 may have resulted in the unusual community in the Grootvloer temporary pool.     

我国正常人共焦激光扫描视神经乳头地形图分析

目的 运用共焦激光扫描检眼镜(LCSO)测定国人(汉族)视神经乳头(ONH)地形图参数的正常值范围,为临床上青光眼的早期诊断及随访提供依据。方法 用HRT(Heidel-berg Retina Tomograph)技术,检测我国(汉族)74只正常眼ONH地形图参数,经统计学处理,制定各参数的均数(Mean)、标准差(SD)、第5、50、95百分位数(P5、P50、P95)值。并分析ONH参数与种族、性别相关的差异;与年龄、眼别相关的差异作了探讨。结果 国人(汉族)ONH参数的正常值(Meen±SD)为视盘面积(DA)2.34±0.46;视杯面积(CA)0.48±0.28;杯盘面积比(CDR)0.2±0.1;盘沿面积(RA)0.18±0.38;视杯体积(CV)0.1±0.1;盘沿体积(RV)0.5±0.19;平均杯深(MeCD)0.18±0.08;最大杯深(MxCD)0.57±0.21;杯形测量(CSM)-0.25±0.06;曲线高度变化(HVC)0.41±0.12;平均视网膜神经纤维层厚度(mRNFLt)0.27±0.08;视网膜神经纤维层交叉段面积(RNFLcsa)1.47±0.48;标准化参考平面高度(RH)0.29±0.11。各参数P5、P50、P95值分别为DA1、59、2.35、3.05;CA0.11、0.41、0.89;CDR0.06、0.19、0.36;RA1.28、1.82、2.49;CV 0.002、0.06、0.29;RV0.25、0.45、0.84;MeCD 0.05、0.18、0.34;MxCD 0.21、0.59、0.95;CSM-0.35、-0.25、-0.14;HVC 0.23、0.4、0.62;mRNFLt0.14、0.27、0.42;RNF     

广西三江侗族儿童青少年头面部发育指标分析

本文对广西三江侗族自治县的 7— 16岁乡村侗族男女中、小学生 2 0 87名 (男 10 5 5 ,女 10 32 )的头面部9项指标进行测量 ,并计算有关指数 ,分析和比较了儿童青少年容貌特征发育与年龄增长的关系。根据头面部指数分型 ,确定了广西三江侗族自治县侗族儿童青少年的头面部形态。依各项指数 ,侗族儿童青少年多属圆头型 ,高头型 ,阔头型及阔面型。