中国龙胆科一新属——扁蕾属

Gentiana was originally proposed by Tournefort in 1700. Linnaeus adopted this generic name in his “Genera Plantarum” published in 1737. He divided the genus into seven groups on the basis of different shapes of corolla and forms of floral appendages. In his “Species Plantarum” he reorganized them into three artificial ones.  Forty years later, Moench established a new genus, Gentianella under which he described G. tetrandra as the type of his new genus.  In the view of identity of Gentianella tetrandra with Gentiana campestris L., it is evident that Gentianella represents only some plants formerly included in Gentiana at Linnaeus time.  In 1796, Froelich’s monograph on Gentiana appeared.  In his work four sections were represented and one of them was Crossopetalum.  In 1845, Grisebach also published a monograph of  Gentianaceae and recorded fifteen sections of which Amarella and Imaicola are two of his seven proposed ones. In 1888, Huxley studied the floral structure of Gentianaceae  in relation with pollination mechanism and, accordingly, divided the family into two  main groups, one with epipetalous glands, the other with glands at the base of the ovary.  In each group, four types of flowers were found.  He concluded that Gentiana was a  complex genus on account of presence of four different types of flowers in this group,  and suggested that many species of the genus should be separated out to form some smaller  generic categories.  Six years after, Kusnezow in his monograph divided Gentiana into  two subgenera Eugentiana and Gentianella.  In his system, subgenus Eugentiana consists  of ten sections and the Gentianella, seven.  He contributed much to the systematic  treatment of Eugnetiana but little to that of Gentianella.  He maintained the genus  Gentiana in a broad sense.  With increased knowledge of this group in the last thirty years, a number of botanists were able to make a clearer delimitation of true Gentiana  and its allies and treated them in more natural way.  Moench’s genus Gentianella was  rerised.  In 1936, H. Smith separated Megacodon from Gentianella as a genus.  In the  present paper, the writer suggests a generic name Gentianopsis for the section Crossopetalum in the same Genus. This new genus is characterized by (1) its large and somewhat flattened ellipsoidal   flower bud, (2) two dissimilar pairs of calyx lobes which are distichously imbricate in  aestivation, (3) four triangular, ciflated intracalyx membranes at the base of and  alternate with the calyx lobes, (4) distinct gynophore and (5) enlarged stigma. While  in typical Gentianella represented by section Amarella, the flower buds are small and terete, a laciniate corona is usually present, and the calyx-lobes are leafy, lanceolate, imbricate, and not provided with intracalyx membrane.       Besides the morphological characters mentioned above, the anatomical structure of  the floral parts is also a significant generic criterion.  In Gentianopsis, eight vascular  bundles are present in calyx, representing four dorsals and four fused ventrals.  In each  corolla-lobe there are five bundles.  In the body of ovary six bundles are present.  The ovule bearing surface is extensive covering nearly to entire surface of the ovary wall with  the exception of a narrow longitudinal zone along the dorsal bundle.  In Gentianella, calyx bundles are three in each lobe, without fusion of the ventrals.  In each corolla- lobe, the bundles are three instead of five as in Gentianopsis but the lateral ones branch once dichotomously after entering the base of corolla. In the body of ovary only four main bundles are present due to the fusion of smaller ventral ones.  The placentation is confined to the region of the ventral bundles.        Phylogenetically Gentianopsis and Gentianella may be regarded as closely reIated and may represent branches of a common line with Gentianopsis standing at a lower level, Gentianella being more advanced. In Gentianella the number of bundles in the corolla segments and ovary wall are reduced by partial or complete fusion and the distribution of ovules is confined only to the region of the ventral bundles.  However, in the calyx of Gentianopsis there is fusion of ventral bundles, whereas the correspound- ing bundles in the Gentianella remain separate.  The Gentianopsis-Gentianella line on the one hand and the Gentiana line on the other may come again from a common acestral stock.  Gentiana possesses only three bundles in each corolla-lobe.  A variety of plicate between corolla lobes except in case of Gentiana lutea and intracalyx membrane above the throat of calyx-tube are also the common structures in Gentiana.  Thus the pollination mechanism is highly specialized in the genus.  As far as we know, in Gentiana the glandular appendages usually exist at the base of ovary.  If those nectarial processes are correctly interpreted as the representatives of staminodes, gentiana would, undoubtedly, be derived from an ancestral  form with  hypogynous  diplostemonous androecium, and bears no direct relationship to Gentianopsis or Gentianella in which the glands are epipetalous.  It may be reasonable to conclude the Gentiana and Gentianopsis- Gentianella line are two parallel derivatives from a common ancestor which has the floral characters of two series of hypogynous stamens. Gentianopsis and Gentianella may represent branches of a common line with Gentianopsis standing at a lower level, Gentianella being more advanced. Their relations may be diagrammed below:                                                       Gentianopsis                                                                                                                               Gentianella Common ancestor                                                       Gentiana        This new genus consists of fourteen species and two varieties in the world.  Onlyeight species and two varieties are represented in China. They are G. barbara, G. barbatavar. sinensis, G. grandis, G. scabromanginata, G. paludosa, G. nana, G. longistyla,G. lutea, G. contorta, and G. contorta var. Wui.     The species of present genus occur in the alpine regions of North Hemisphere.  InChina t,hey are distributed in Kokonor, Kansu, Shensi, Shansi, Chahar, Hopei, Manchuria,Hupeh, Szechuan, Sikang, Tibet, and Yunnan. G. Yabei (Takeda et Hara) is foundin Japan, G. detonsa (Bott&) in North Europe, G. ciliata (Linn.) in South Europe,G. crinita (Froel.) G. procera (Holm.) and G. degans (A. Nels) in North America.G. barbata is the most widespreading species and reported in Sibiria and China.G. contorta (Royle) is a common plant in Himalayan mountaineous range, China andNorth part of India.     The species and varieties cited in this paper are as follows:           t.  Gentianopsis barbata (Froel.) comb. nov.           la. Gentianopsis barbata (Froel.) var. sinensis, var. nov.          2.  Gentian opsis grandis (H. Sm.) comb. nov.          3.  Gentianopsis scabromarginata (H. Sm.) comb. nov.          4.  Gcntianopsis paludosa (Munro) comb. nov.          5.  Gentianopsis nana sp. nov.          6.  Gentianopsis longistyla, sp. nov.          7.  Gentianopsis lutea, sp. nov.     

马兜铃科的地理分布及其系统

马兜铃科基本是一个热带科。  东亚的横断山至华南一带是其原始分布与分化中心，热带美洲是其次生分布与分化中心。科的形态演化趋势是花被由分化的双被到不分化的单被，由分离到合生，由杯状到管状；雄蕊由多数到少数，由分离到与雌蕊结合成为合蕊柱；于房由半下位到完全下位；果实由蓇葖状蒴果到蒴果。马兜铃科分2亚科4族6属。     

南海北部早第三纪流沙港组孢粉组合

In the northern part of South China Sea, including Tonkin Gulf, Hainan lsland, Leizhon Peninsula and some basin of Guangdong  Province,  Paleogene  deposits  are composed of three formations: the Weizhon, the Liushagang and the Changliu forma- tions arranged in descending order.  The paper on the palynoflora of the Weizhon Formation (early and middle Oligocene) is in press[2].  This paper deals only with the palynoflora of the Liushagang Formation, with may be divided into four main stages:       The first stage is represented by Monocolpollenites tranquillus and Crassoretitri- letes sp., assigned to early Eocene The second stage is characterized by Salixipollenites, Momipites triletipollenites and Operculumpollis.  Its age is middle Eocene.  The third stage is dominated by some species of Quercoidites  and  Ulmipollenites  and  also characterized by the presence of Platycaryapollenites  and Prominangularia  dogying- ensis, This sporo-pollen assemblage suggests a late Eocene in age.  The fouth stage is marked by profusion of some alga of brockish water, such as Rugasphera corrugia, Granodiscus gronulatus and some pollen types  of  Liquidambarpollenites   minutus, Multiporopollenites puctatus and Tricolporopollenites minutus.  The age of the last stage is assigned to early oliocene.       In generaly, the palynoflora of the Liushagang Formation is quite different from that of the Weizhou Formation.  The main types of spores and pollen are common with those found in Europe and North America of the same age, while the Weizhou Formation has many elements common both in this region and Borneo.       During Eocene and early Oligocene this area was  of continental  phase with brackish basins. At the beginning the climate was rather moist and hot, but then itbecame moist and warmtemperate.     

横断山地区兰科植物区系的研究

兰科在横断山地区是维管束植物中的大科之一，共有91属，363种及9变种。 4属为我国特有属，其中1属为本地区所特有；155种及9变种为我国特有种。  其中69种及5变种为本地区所 特有。本文对属、种进行了分析，并对全部种的分布格局作了详细的介绍，概述了本地区兰科植物的区系组成及特点。本文从兰科植物属、种的分布提出了四川峨眉山是东亚植物区中划分中国-喜马拉雅植物亚区和中国-日本植物亚区的分界线上的一个重要的点的看法。     

Who is a Modeler?

Many standard philosophical accounts of scientific practicefail to distinguish between modeling and other types of theoryconstruction. This failure is unfortunate because there areimportant contrasts among the goals, procedures, and representationsemployed by modelers and other kinds of theorists. We can seesome of these differences intuitively when we reflect on themethods of theorists such as Vito Volterra and Linus Paulingon the one hand, and Charles Darwin and Dimitri Mendeleev onthe other. Much of Volterra's and Pauling's work involved modeling;much of Darwin's and Mendeleev's did not. In order to capturethis distinction, I consider two examples of theory constructionin detail: Volterra's treatment of post-WWI fishery dynamicsand Mendeleev's construction of the periodic system. I arguethat modeling can be distinguished from other forms of theorizingby the procedures modelers use to represent and to study real-worldphenomena: indirect representation and analysis. This differentiationbetween modelers and non-modelers is one component of the largerproject of understanding the practice of modeling, its distinctivefeatures, and the strategies of abstraction and idealizationit employs.

1 Introduction

2 The essential contrast

2.1 Modeling

2.2 Abstract directrepresentation

3 Scientific models

4 Distinguishing modeling from ADR

4.1 The first and secondstages of modeling

4.2 Third stage of modeling

4.3 ADR

5 Who is not a modeler?

6 Conclusion: who is a modeler?

     

浙江产7种菝葜的染色体研究

本文报道浙江产菝葜属smilax 7个种的染色体数目和核型。S．nipponica有两种核型，2n＝   26和2n=32，均为3B型，但后一种细胞型的雄株的第一对染色体大小不等，可能为性染色体；S.   riparia 2n=30，属3B型；S．siebodii n＝16；S. china有两个染色体数目，2n＝96 和n＝15；   S. davidiana 2n=32，属3B型，对减数分裂MI的观察发现n＝16；S．glabra 2n=32，亦属3B   型：S. nervo-marginata var．liukiuensis 2n=32，属3C型。讨论了种间在核型上的差异、属的基数、   核型演化趋势和性染色体等问题。     

中国薯蓣属根状茎组系统分类的初步研究

   本文根据我国薯蓣属(Dioscorea L．)根状茎组(Sect.  Stenophora Uline)的外部形态特征、细胞染色体数、花粉形态、植物化学成分、地理分布等的规律，证明根状茎组是该属中的一个比较原始的自然类群：1．具横走的多年生地下根状茎，其它组是一年生或多年生的块茎；2．大部分是2倍体，其它组是多倍体；3．花粉粒单沟型，外壁纹饰网纹或颗粒条纹，其它组为双沟型，外壁纹饰网纹；4．含甾体皂甙元(steroidal sapogenin)，其它组不含。   我们的研究观察证明，N．N．TepaCNMeHKO根据R.Knuth系统(1924)提出的薯蓣皂甙元在该属中无分布规律的说法是无充分依据的。   本文讨论了某些组或种的划分及系统位置：取消sect.Illigerestrum Prain et Burk.；将马    肠薯蓣(D．simulans Prain et Burk．)改属根状茎组；触丝薯蓣(D．tentaculigera Prain et Burk.)应列入顶生翅组  (Sect．shannicorea Prain et Burk．)，  并提出了盾叶薯蓣  (D. zingiberensis  Wright)和穿龙薯蓣(D．nipponica Makino)种的划分和定名的意见。     

A modified PID controller (PIIσβD)

The purpose of this study is to modify the traditional PID controller in order to improve its performance (stability and tracking) by changing the length of integration interval. The performance of the traditional PID controller was improved by changing the length of integration interval to make the most of the returns of the PID and PI_σD controllers. The asymptotic stability domain, in terms of the feedback gains, is derived for systems of second order using the modified controller which will be identified as PII_σ^βD. Comparing this controller with the traditional PID controller and PI_σD controller proposed in [1], it proves that it is more accurate and more stable. For illustration and comparison, two examples have been simulated to evaluate the performance of the modified controller. All simulation results indicate that the modified controller is better than the traditional PID controller and the PI_σD controller from the accuracy and stability point of view.     

中国第三纪植被和植物区系历史及分区

被子植物的发展(或称辐射)是与古气候、古地理环境密切相关的，诸因素的变化相互影响及制 约，形成植物发展的阶段性。这种阶段变革及划分与传统的地质时代划分——断带，不尽一致，因而讨论 植物地理分区问题应以发展的不同阶段为基础，致使分区更为合理。     在晚白垩纪中晚期，被子植物已成为植物区系中的优势成分，从它出现以来的发展演化大致可划分 为四个阶段：(1)初始期  被子植物初次出现，具有叶形小、叶边全缘、叶脉缺乏规律性、脉级分化程度低 等原始性特点，同时在区系中的种数及个体数量均为极少数，此时大约在早白垩纪的中晚期；(2)极盛时 期被子植物发展具有一定规模至占绝对优势，此时叶形增大，叶脉有了规律性，脉级分化逐渐完善，在 植物区系中所占比例达40％一60％，以致占绝对优势，主要科属出现了，时间在晚白垩至老第三纪；(3) 草本植物繁盛阶段  由于在新第三纪时气候逐渐转凉，早期的一些木本植物消灭了，以草本植物渐增多 至大量扩散为特点，时间约在中新世至上新世；(4)第四纪阶段  此时我国由于山岳冰川随全球性气候 冷暖变化而进退，影响植物的分布及发展，植物区系的总面貌与现代接近或略有差别。   本文亦重点讨论了植物发展的第二、第三阶段的植物地理分区。     

中国植物区系中的特有现象——特有属的研究

本文对我国种子植物特有属作了初步研究，提出如下几点粗浅的看法：     1．根据我国各特有属的现代地理分布格局，大部分特有属具有明显的温带性特点。     2．我国特有属在水平分布上具有极不均匀的特点。各特有属的广布程度都很低，生态特     化现象十分明显。在垂直分布上，则主要分布于中海拔地区。特有属数目并不随海拔增高而     增多。     3．根据特有属分布的密集程度和分布区边界的密集交叠情况，划定了三个特有属分布中    心，即川东—鄂西中心, 滇东南—桂西中心和川西—滇西北中心。前二中心可能是残遗中心，后一中心则可能为分化中心。     

我国生鲜农产品电子商务冷链物流现状与发展研究

通过对648家电商网站中的111家生鲜农产品电商网站提供冷链物流服务情况的调查,对其冷链物流概况、冷链物流设施设备的使用情况、冷链物流覆盖区域、物流模式以及冷链物流外包服务商进行研究,并就存在问题从政策、标准、信息技术、设备等方面提出建议与对策。     

Changes in velocity profile according to blood viscosity in a microchannel

Red blood cells (RBCs) are important to dictate hemorheological properties of blood. The shear-thinning effect of blood is mainly attributed to the characteristics of the RBCs. Variations in hemorheological properties alter flow resistance and wall shear stress in blood vessels. Therefore, detailed understanding of the relationship between the hemorheological and hemodynamic properties is of great importance. In this study, blood viscosity and blood flow were simultaneously measured in the same microfluidic device by monitoring the flow-switching phenomenon. To investigate blood flows according to hemorheological variations, the flow rate of blood samples (RBCs suspended in autologous plasma, dextran-treated plasma, and in phosphate buffered saline solution) was precisely controlled with a syringe pump. Velocity profiles of blood flows were measured by using a micro-particle image velocimetry technique. The shape of velocity profiles was quantified by using a curve-fitting equation. It is found that the shape of the velocity profiles is highly correlated with blood viscosity. To demonstrate the relationship under ex vivo conditions, biophysical properties and velocity profiles were measured in an extracorporeal rat bypass loop. Experimental results show that increased blood viscosity seems to induce blunt velocity profile with high velocity component at the wall of the microchannel. Simultaneous measurement of blood viscosity and velocity profile would be useful for understanding the effects of hemorheological features on the hemodynamic characteristics in capillary blood vessels.     

国产乌头属的化学分类

根据二萜生物碱的类型、生物合成、在乌头属植物中的分布，并参照国产乌头属的系统分类、形态演化和地理分布，本文讨论国产乌头属的化学分类。 1．以牛扁碱型成分为主的牛扁亚属和以乌头碱型成分为主的乌头亚属可能在乌头属进化的初期阶段就已分化，各自沿着独立的道路发展。2．乌头亚属包括以下类群：(1)以阿替生型、维特钦型、乌头碱型胺酵和 酯碱为主的保山乌头系，主要分布于国产乌头属近代发展分化中心之一的横断山脉和金沙江流域，可能国产乌头组的近代分化就是由该系发展而来; (2)以乌头碱、中乌头碱、下乌头碱为主的乌头系，为进化程度较高的群，所含乌头碱及尼奥灵显示了该系与保山乌头系的亲缘关系; (3)以乌头碱和松果灵为主的准噶尔乌头系，所含乌头碱和松果灵显示了该系与保山乌头系的亲缘关系; (4)以滇乌碱类酯碱为主的显柱乌头系和蔓乌头系，为进化程度较高的群，其酯碱有别于乌头碱类。3．以阿替生及C19内酯型为主的甘青乌头系及圆叶乌头系，可能为进化早期形成的高山特化类群。4. 以阿替生和C19乌头碱型胺醇为主的露蕊乌头亚属，可能为特化类群。     

峨眉山兰科植物的地理分布和区系特点

 Situated in western part of Sichuan Province, 29°30'N, 103°20'E, the sacred Mt. Emei is one of the well-known large mountains in China. Its summit is about 3100 m ab- ove sea level with a relative height of 2550 m.        The orchid flora in Mt. Emei so far known comprises 47 genera and 109 species, among which 21 are epiphytes, 83 terrestrials and 5 saprophytes (Table 1.)        1.  The vertical distribution of the orchid flora in the mountain. The epiphytic orchids are concentrated in the lower region  below Hongchunping and Wanniansi (1100 m alt.), where there are 20 species, which make over 95% of epiphytic species; the upper limit for the epiphytic orchids is Jiulaodong and Chudian ( 1800 m alt.). The terrestrial orchids also mainly occur at the lower region below Jiulaodong and Chudian (1800 m alt.), where there are 54 species, most of which are found at even lower part of the mountain, below Hongchunping and Wanniansi (1100 m alt.). The tropicas orchids in the mountain, such as Cleisostoma, Vanda, Holcoglossum, Tropiclia, Thunia, Mischobulbum, Ludisia, Anoectochilus, Odontochilus, etc. all grow only at the lower part of the mountain below Hongchunping and Wanniansi (1100 m alt.).        2. The floristic features of the orchid flora in the Mt. Emei.        (1)  The orchid flora in the mountain so far known comprises 47 genera (over 2/3 of the total orchid genera in Sichuan) and 109 species (over 1/3 of the total orchid species in Sichuan). The Mt. Emei is very rich in orchid species, as compared with neighbouring mountains of same magnitude, such as Mt. Shennonjia in western Hubei, Qin Ling in sou- thern Shaanxi, Jinfo Shan in south-eastern Sichuan, and Erlang Shan in western Sichuan.        (2)  The orchids in the mountain are complex in floristic components as indicated below:        1)  Twenty seven species, belonging to 18 genera, are widespread, covering the whole East-Asian region.        2)  Twenty three species, belonging to 15 genera, are the elements of the Sino-Japanese Subregion. Among them 13 species occur only in Japan and eastern China with the mountain ar the westernmost limit, but the other species extend westwards as far as Kangding and ErLang Shan or Baoxing in Sichuan Province.        3)  Forty two species, belonging to 22 genera, are the elements of the Sino-Himala-yan Subregion, with 5 species having their range extending from the Himalayan  region eastwards to Mt. Emei.        4)  Some tropical genera (8 species), belonging to Indo-Malaysian floristic elements, have the mountain as their northern limit of distribution.       The orchid flora of the Mt. Emei contains not only the East-Asian elements, but also some Indo-Malaysian elements, though its composition is mainly of the temperate and subtropical Eastern Asian (Sino-Japanese) ones.        (3)  The orchid flora in the mountain is characterized by geographical vicariation and differentiation.       There are nine species-pairs (belong to genera Calanthe,  Platanthera,  Dendrobium etc.) of the vertical vicarism and six species-pairs (belonging to genera Tropidia, Aneoctochilus, Mischobulbum, Gymnadenia Orchis, etc.) of the horizontal vicarism in the Mt.  Emei.       Remarkable differentiation of orchid flora in the Mt. Emei is shown in the abundance of endemic elements and as clear geographical vicariation.        (4)  There are 8 endemic species and one variety of orchids in the Mt. Emei, more  abundant than in Xizang.      The floristic features of the orchid flora of the Mt. Emei are rich in species, compara tively complex in components, rather prolific in endemic species, and characterized by geographical vicariation and differentiation. The orchid flora in the Mt. Emei mainly consists of the subtropical and temperate East-Asian elements, with a  considerable proportion of tropical elements though.     

湖南岳阳杨树人工林光能利用率动态特征分析

植物光能利用率（Light Use Efficiency,LUE）作为表征植被利用光能合成生物化学能效率的重要指标,直接影响到生态系统生产力。本文使用2006年4月-10月湖南岳阳站通量观测资料,探讨杨树人工林不同时间尺度的光能利用率动态特征。结果表明：①杨树人工林生态系统典型晴天LUE_（30min）存在明显的＂V＂形日变化,其值介于（13.18~45.28）mmol/mol,最低值都出现在中午前后;②5日累计光能利用率（LUE_5）季节动态呈双峰型变化,峰值分别出现在5月初（42.57mmol/mol）和7月中旬（57.50mmol/mol）;③月尺度光能利用率（LUEmon）分别为24.79、27.85、20.95、42.27、32.60、24.91和10.47mmol/mol,最大值出现在7月份,且LUE_（mon）最大值较LUE5和LUE_（30min）低,最小值较LUE5和LUE_（30min）高。这些结果将为提高生态系统资源的利用提供重要的定量化依据。     

Molecular characterization of CHST11 and its potential role in nacre formation in pearl oyster Pinctada fucata martensii

BackgroundC4ST-1 catalyzes the transfer of sulfate groups in the sulfonation of chondroitin during chondroitin sulfate synthesis. Chondroitin sulfate consists of numerous copies of negatively charged sulfonic acid groups that participate in the nucleation process of biomineralization. In the present study, we obtained two CHST11 genes (PmCHST11a and PmCHST11b) which encoded the C4ST-1 and explored the functions of these genes in the synthesis of chondroitin sulfate and in the formation of the nacreous layer of shells.ResultsBoth PmCHST11a and PmCHST11b had a sulfotransferase-2 domain, a signal peptide and a transmembrane domain. These properties indicated that these genes localize in the Golgi apparatus. Real-time PCR revealed that both PmCHST11a and PmCHST11b were highly expressed in the central zone of the mantle tissue. Inhibiting PmCHST11a and PmCHST11b via RNA interference significantly decreased the expression levels of these genes in the central zone of the mantle tissue and the concentration of chondroitin sulfate in extrapallial fluid. Moreover, shell nacre crystallized irregularly with a rough surface after RNA interference.ConclusionsThis study indicated that PmCHST11a and PmCHST11b are involved in the nacre formation of Pinctada fucata martensii through participating in the synthesis of chondroitin sulfate.     

西藏高原植物区系中特有属的研究

The Xizang (Tibetan) flora with numerous endemics is of importance in Chi- nese flora.   According to recent statistics there are in Xizang 27 genera of  spermatophytes endemic to China, being only 2.25% percent of the total number of genera in the Xizang flora. Four of them are regarded as palaeoendemics (14.81%) and the others as neoendemics (85.19%). These endemic genera, of 30 species and 3 varieties, belong to 17 families, of which, Umbelli- ferae contains 6 genera, 7 species and 3 varieties; Compositae has 6 genera and 7 species, and Gentianaceae 1 genus and 2 species.  All the other families each comprises one genus with a single species.       The cosmopolitan families together comprising 14 genera with 15 species have the highest perecentage (52.92%) and the tropical ones (5 families, 5 genera with 5 species) come to the next (29.42%), followed by the temperate ones (3 families, 10 genera with 10 species) (17.66%). It shows that these endemic genera are obviously related to the tropical flora and temperate one in essence.        According to the number of species, the genera endemic to China and occurring in Xi- zang flora may be grouped as fallows. Monotypic endemic ones 14 (51.85%) Ditypic endemic ones 6 (22.22%) Oligotypic endemic ones 4 (14.81%) Small endemic ones 3 (11.11%)        The formation of the endemic genera is correlated with the topography, climate and en- vironmental conditions, and they may have resulted from the diversification in geography and climatic influence for a long time.  The southeastern part of Xizang Plateau is of very diverse ecological conditions, with the adequate precipitation, which may explain the concentration of these endemic genera in this region.        The largest similarity coefficient (38.30%) of the genera endemic to China and occurring in Xizang is with those in Qinghai Plateau, next, with those in Yunnan and in Sichuan pro- vinces (both 27.60%), which shows that these endemic genera are related to the floras of the regions mentioned above.        The difference in the horizontal distribution of these endemic genera is obviously between the southern and northern parts of Xizang Plateau.  The vertical distribution of the genera is also rather obvious, from 800 m to 5200 m above sea level, but concentrated in the zone of 3000 m to 4500 mm.  Therefore their occurrence in Xizang is not only affected by the historical environmental conditions but also controlled by the horizontal and vertical distribution.      The origin and evolution of some endemic genera, such as Psammosilene, Parateropyrum, Sphaerotylos, Salweenia, Ajaniopsis, Xizangia, Sinoleontopodium, are discussed in this paper.      Parateropyrum, a monotypic palaeotropic endemic, belongs to the tribe Atraphaxideae in- cluding Atraphaxis, Calligonum and Pteropyrum.  It may be a comparatively advanced group in the tribe, and is closely related to the genus Pteropyrum  which is  distributed in western Asia.  The genus Parapteropyrum has possibly survived as a palaetropic-tertiary  relic in this region.      Sphaerotylos, a member of the subtribe Sphaerotylinae, the tribe Boehmerieae in the family Urticaceae, is a comparatively primitive genus in the tribe Boehmerieae so far known.  As the other subtribes, such as Boehmerinae, Sarconchlamydinae, Orecnidinae and Maoutinae, are dis- tributed in the tropics, rarely in the subtropics, the genus is no doubt a palaetropic -tertiary relic.      Sinoleontopodium, belonging to the tribe lnuleae in Compositae, is also related to the ge- nus Leontopodium.  It is probable that the genus Sinoleontopodium arised later than the other.       We come to the conclusion that the southern part of Xizang Plateau is also one of thecentres of the origin and differentiation of genera endemic to China.