MOLECULAR STRUCTURE OF PLANT FIBERS DETERMINED BY X-RAYS

It has been shown that the wall of the plant fiber is probably built up of unit groups of atoms which have assumed the form of a space lattice. The elementary cell of the lattice is an orthorhombic structure with the dimensions 6.10 x 5.40 x 10.30 Å.u., and contains two unit groups equal in size to two C₆H₁₀O₅ groups. The crystallographic unit cell would contain 4 of these elementary cells and would be represented by Fig. 9 rather than by Fig. 3. The groups of atoms, C₆H₁₀O₅, are arranged in parallel chains running lengthwise of the fiber. In each chain the odd numbered groups have a different orientation from the even numbered. The chains, parallel to one another are spaced 6.10 Å.u. in one direction and 5.40 Å.u. at right angles to that. In these two directions the odd numbered chains also would have a different orientation from the even numbered. On account of the cylindrical shape of the fiber, the elementary cells are arranged in the form of concentric cylinders or layers. The dimensions of the fibers are such that the fiber wall is about 40,000 elementary cells in thickness, or in other words, the fiber is composed of that many concentric layers. If it could be magnified sufficiently, a cross-section of a fiber would show the end view of each cylinder as a dotted circle. The dots, representing the unit groups of atoms, would have considerable uniformity of spacing in both the tangential and the radial directions, 6.10 Å.u. in one and 5.40 Å.u. in the other. The structure could not be as rigidly exact as might be inferred, since the wall is deposited more or less rhythmically during a period of several days or weeks* in which adjustments in the arrangement of the unit groups undoubtedly occur. It is common knowledge that the fibers, under the microscope, rarely appear as true circles on cross-section; usually they appear as irregular, many-sided polygons and the wall thickness is normally uneven. For our purpose it is simpler to think of the fiber as composed of concentric cylinders with diameters so large in proportion to the size of the unit groups that in relatively large segments they closely approach the parallelism of the planes of a rectangular lattice, sufficiently close to be capable of producing diffraction patterns. Although these conclusions seem to be in agreement with the diffraction patterns obtained from various positions of a bundle of approximately parallel fibers, the fact must not be overlooked that the structure cannot be proved with as great certainty as can the structure of a well formed crystal. The very nature of the fiber, its cylindrical shape, and the many internal adjustments which must take place, militate against a clean-cut demonstration. Models, made more or less to scale, were used in working out this structure. The unit group was constructed according to Irvine''s suggestion that all the groups are glucose residues. An intensive study is now under way in which an attempt is being made to bring the models into agreement with the chemical and physical properties of the cellulose fibers and with the diffraction patterns. A report on that part of the work will soon be submitted for publication.     

THE MODIFICATION OF ANTIBODIES BY FORMALDEHYDE

Certain strains of bacteria which have only minimal zeta potentials over a wide range of pH, and upon which surface deposits can be formed, afford a favorable means of studying certain chemical and physical properties of the surface deposits. Films of specific antibody-globulin upon these bacteria possess basic groups which can combine with formaldehyde. Combination of these groups with HCHO under the conditions of the present experiments shifts the isoelectric point of the sensitizing film toward the acid side by about 0.6 to 0.8 pH unit, and reduces the agglutinating tendency of the sensitizing film. Antibodies may be formalinized before combination with antigen without marked change in their specific combining affinities. The properties of the sensitizing films are similar whether formol treatment occurs before or after the antigen-antibody combination. The nature of the basic groups has been discussed.     

番荔枝科10种植物叶表皮结构的研究

利用光学显微镜和扫描电子显微镜,对番荔枝科10种植物的叶表皮结构进行了观察,结果如下：表皮细胞近等径多角形或不规则形,垂周壁直,弧形,浅波状,波状或深波状,瓜馥木和香港瓜馥木叶片远轴面表皮细胞平周壁形成乳突,有的植物表皮细胞内具棱晶或晶簇,气孔器全部为平列型,具2－6个副卫细胞,除鹰爪花近轴面,远轴面均具气孔器外,其它9种植物的气孔器仅分布在远轴面,有的植物还具有双气孔器或败育的气孔器类型。除圆滑番荔枝外,其它9种的表皮均具表皮毛,表皮毛有单细胞毛,单列多细胞毛,2列多细胞毛,棍棒状毛和星状毛等类型,研究结果表明,10种植物的表皮细胞形状,垂周壁的式样,平周壁是否乳突,表皮细胞内晶体的有无及其类型,近轴面是否具气孔器,表皮毛的类型等方面存在着种间差异,这些特征可以作为种间甚至属间分类和系统关系探讨的依据。     

高寒草原优势种叶片结构变化与生态因子的关系

 为了揭示青藏高原高寒草原优势物种青藏苔草（Carex moorcroftii）和紫花针茅（Stipa purpurea）对高原特殊环境的适应性,该文研究了 它们的叶片结构在自然环境梯度下的变化以及这些变化与生态因子之间的关系。结果表明：这两个物种叶片的大多数结构特征在各个样地间变 化显著,其结构特征与环境因子间存在显著的相关关系。紫花针茅叶肉细胞大小随土壤有效K含量的增高而减小,下表皮细胞厚度和韧皮部面积 随生长季云盖度的增高而增加,单一导管半径和导管平均面积随生长季月均湿度的增加而增大;青藏苔草上表皮细胞厚度随生长季月均最低温 的降低而增厚,泡状细胞厚度（径向直径）随大陆度的增强而增加,上表皮细胞大小随土壤pH值的增大而增大,导管总数和韧皮部面积随土壤 速效P含量的增高而增加。青藏苔草的保护组织、光合组织以及综合指标变异系数明显大于紫花针茅,仅维管组织指标变异系数小于紫花针茅。     

中国春黄菊族植物叶表皮结构的研究

本文对分布在中国的春黄菊族(Anthemideae)中的25属98种植物叶的表皮结构进行了观察。1.毛状体的类型适于作为本族自然群、属、亚属、组或系的分类特征。2.轴型、半平列型和螺旋型等复合结构的气孔适于作属以下各单位的分类依据。3.表皮细胞的大小、气孔的保卫细胞长度和 T 型-毛的顶端长度等,这些只是数量特征,在本族分类上意义不大。     

COMPARATIVE LEAF STRUCTURE OF SEVERAL SPECIES OF HOMOSPOROUS LEPTOSPORANGIATE FERNS

The structure of the mature leaves of 13 species from 9 families of homosporous leptosporangiate ferns was examined by light and electron microscopy. In 11 species (Adiantum pedatum L., Athyrium angustum Roth., Cyathea dregei Sm., Lygodium palmatum Sw., Mohria caffrorum (L.) Desv., Oleandra distenta Kuntae, Pellaea calomelanos (Sw.) Link, Pityrogramma calomelanos (L.) Link var. austro-americana (Domn.) Farw., Trichomanes melanotrichum Schlechtend., Vittaria guineensis Desv., and Woodwardia orientalis Sw.) the lamina veins are collateral; in two (Phlebodium aureum and Platycerium bifurcatum), bicollateral as well as collateral veins are present. The vascular bundles in the midribs of C. dregei and those in the petioles and midribs of Phlebodium and Platycerium are concentric. All of the vascular bundles in the homosporous leptosporangiate ferns studied are delimited by a tightly arranged cylinder of endodermal cells with Casparian strips. Within the veins without parenchymatic xylem sheaths, some sieve elements commonly abut tracheary elements with hydrolyzed primary walls. The majority of vascular parenchyma cells contact both sieve elements and tracheary elements, although some parenchyma cells are associated with only one type of conducting cell. Transfer cells (parenchyma cells with wall ingrowths) occur in the veins of 6 species examined. Most of the vascular parenchyma cells, however, have no distinctive structural characteristics. The sieve elements of the homosporous leptosporangiate ferns are very similar structurally and each consists of a plasmalemma, a parietal, anastomosing network of smooth endoplasmic reticulum (ER), and variable numbers of refractive spherules, plastids and mitochondria. The sieve elements of L. palmatum also contain plasmalemma tubules. The parenchymatic cells of the leaf (mesophyll, endodermal and vascular parenchyma cells) are united by desmotubule-containing plasmodesmata. The sieve elements are connected to each other by sieve pores and to parenchymatic cells by pore-plasmodesma connections. The sieve-area pores contain variable amounts of membranous material, apparently ER membranes, but do not occlude them. These membranes commonly are found in continuity with the parietal ER of the lumen. Based upon the relative frequencies of cytoplasmic connections between cell types, the photosynthates may move from the mesophyll to the site of phloem loading via somewhat different pathways in different species of homosporous leptosporangiate ferns.     

以叶盘为外植体的白桦的再生

从不同的激素组成(BA, K T, 2, 4~D, NAA, GA₃)、基本培养基(MS, WP)、外植体放置的方向性进行了实验, 建立了以白桦叶盘为外植体的再生系统。当叶盘向轴面朝下放置在培养基上时, 三周后, 从叶盘边缘生出不定芽。不定芽的诱导率为64%, 平均每片叶盘可生出6 个不定芽。叶盘再生系统的建立为白桦的遗传转化提供了前提。     

魔芋葡甘露聚糖化学结构及改性研究进展

本文综述了魔芋葡甘露聚糖的理化性质、化学结构及改性的研究进展