MEDULLARY BUNDLES IN THE GENUS DAHLIA AND THEIR POSSIBLE ORIGIN

Davis , Edward L. (U. Massachusetts, Amherst.) Medullary bundles in the genus Dahlia and their possible origin. Amer. Jour. Bot. 48(2): 108–113. Illus. 1961.—The system of medullary bundles which extends throughout the stem and into the leaves and branches in D. lehmanni is described. It is suggested that this system may have arisen from leaf traces and that the condition in D. scapigera var. scapigera f. merckii and D. coccinea, in which leaf traces fail to develop secondary tissue while adjacent bundles are increasing in diameter, may represent the incipient stage of development of medullary bundles within the genus. The correspondence between the occurrence of medullary bundles and the sectional division of the genus on taxonomic grounds by Sherff is noted.     

PARASITES AND THE EVOLUTION OF SELF-FERTILIZATION

Abstract.— Assuming all else is equal, an allele for selfing should spread when rare in an outcrossing population and rapidly reach fixation. Such an allele will not spread, however, if self‐fertilization results in inbreeding depression so severe that the fitness of selfed offspring is less that half that of outcrossed offspring. Here we consider an ecological force that may also counter the spread of a selfing allele: coevolution with parasites. Computer simulations were conducted for four different genetic models governing the details of infection. Within each of these models, we varied both the level of selfing in the parasite and the level of male‐gamete discounting in the host (i.e., the reduction in outcrossing fitness through male function due to the selfing allele). We then sought the equilibrium level of host selfing under the different conditions. The results show that, over a wide range of conditions, parasites can select for host reproductive strategies in which both selfed and outcrossed progeny are produced (mixed mating). In addition, mixed mating, where it exits, tends to be biased toward selfing.     

猴及人胎儿延髓内脏带的化学神经解剖学

本实验采用免疫组织化学ＡＢＣ法,观察儿茶酚胺类（以酪氨酸羟化酶－ＴＨ作标记物）、５－羟色胺及神经肽（Ｐ物质、亮氨酸－脑啡肽、胆囊收缩素、神经肽Ｙ、生长抑素）在猴及人胎儿延髓内脏带的分布及形态特点。结果发现,上述物质均程度不同地集中分布于猴及人胎儿延髓内脏带,即位于延髓中尾段的一条从背内侧至腹外侧的弧形带状区。这表明猴及人胎儿延髓内脏带是一个相对独立的机能结构区,其化学构筑具有独特特点。     

昆虫纲的历史发展

—、前言 生物是发展的,任何生物都有它的历史发展过程,本篇所要讨论的是昆虫纲在历史发展过程中的几个最主要的、关键性的阶段,特别是这些阶段之间的继承和联系关系。     

THE PLATYCARYA PERPLEX AND THE EVOLUTION OF THE JUGLANDACEAE

We report on the leaves, fruits, inflorescences, and pollen of two fossil species in the genus Platycarya. The association of these dispersed organs has been established by their repeated co-occurrence at a large number of localities, and for two of the organs (fruit and pistillate inflorescence, and pollen and staminate inflorescence) by apparent organic attachment of compression fossils. Each of the two species can be distinguished by characteristics of all the known megafossil organs. We also review the fossil record of dispersed platycaryoid fruits and inflorescences, recognizing three additional species of Platycarya and two of Hooleya. Two of the fossil Platycarya species are morphologically very different from the living Platycarya strobilacea Sieb. et Zucc., but they show the diagnostic features of the genus. Hooleya is a generalized member of the Platycaryeae that is probably close to the ancestry of Platycarya. The two Platycarya species known from multiple organs provide a remarkable example of mosaic evolution in which fertile and foliar structures have attained different levels of morphological specialization. The leaves, often considered the most plastic of plant organs, retain several features that are otherwise seen only in the Engelhardieae. These similarities in leaf architecture between the fossil Platycarya species and Engelhardieae are advanced features for the Juglandaceae, and thus indicate a sister-group relationship between the two lines. In contrast to the leaves, the fruits, inflorescences, and pollen of the fossil Platycarya species are almost as specialized as those of the extant P. strobilacea and bear little resemblance to the same structures in other genera of the family. The morphology, taphonomy, sedimentary setting, and geographic and stratigraphic distribution of three of the fossil platycaryoid species suggest that they were wind-dispersed, early successional plants that grew in thickets. This habit is retained by Platycarya strobilacea and is typical of many of the amentiferae (e.g. Myricaceae, Betulaceae). The r-selected life-history pattern of the Platycarya line may well have contributed to its low diversity through geologic time.     

罂粟科植物的分类,进化与分布

罂粟科有38属约700种,作者通过对科内各属的研究,根据其主要器官(雌蕊、雄蕊,花被、果和种子)的进化趋势,重新排列科内的分类系统,在3个亚科下,包括8个亚族。在此基础上,讨论各属可能的演化关系,分析它们的分布规律,最后探讨本科的起源。