摘要:

SummaryAnomalous distribution of the Southern Hemisphere floras has long been recognized, and many explanations have been proposed. The occurrences of plants, modern or fossil, rarely point to a unique mode of distribution. A synthesis of pertinent information drawn from many disciplines (geonomy) is required to determine a most probable explanation. Recent studies of crustal mechanics by geophysicists show that sea‐floor spreading can serve as an adequate mechanism for continental drift and can be important in explaining the distribution of ancient plants of the Southern Hemisphere.The PermianGlossopterisflora of southern continents contrasts strikingly with the Permian flora of the Northern Hemisphere. The identity of the northern flora that was contemporary with theGlossopterisflora was controversial for many years because of the great degree of isolation existing between the two floras. The botanical relationships of the glossopterids are still imperfectly established, particularly with reference to foliage occasionally found in northern areas or in deposits younger than Permian. Fertile structures of glossopterids seem to provide the only reliable basis for determining botanical relationship. TheGlossopterisflora is, in general, extremely distinctive and consists taxonomically of a relatively small array of plants which occurs over an exceptionally large area. It represents an ecologic assemblage with both climatic and edaphic implications.A tentative Permian Gondwanaland reconstruction is presented that is somewhat more condensed than other reconstructions; the area thus reconstructed is more likely to have had a reasonably consistent, seasonal temperate climate in keeping with consistent similarities of theGlossopterisflora. According to this interpretation, most of the present area of the Indian Ocean seems to have been occupied by Permian Gondwanaland. The ridges and rises as recently mapped across the Indian Ocean floor are incompatible with foundered continents or isthmian links, but they can be interpreted as reflecting an historical sequence in sea‐floor spreading that can account for the present dispersal of Gondwana continents.

ISSN:0040-0262    

DOI:10.2307/1219279

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryGeologically India is divisible into three units (1) Peninsular, (2) Extra‐Peninsular and (3) Jndo‐Gangetic Plain. The Tertiary floras of India can conveniently be divided into two groups — Palaeogene and Neogene. As known today, Palaeogene floras are found only in the Peninsular India, while Neogene occur in both the Peninsular and extra‐Peninsular regions. They are predominantly tropical floras, made up of genera now largely confined to the Old World.A notable feature of the Indian Palaeogene is the occurrence of a few southern hemisphere taxa which may recall the pre‐Cenozoic relationships between India and the Gondwana continents to the south.The London Clay flora shows noticeable general resemblance with the Indian Palaeogene. This feature is discussed taking into account the Tertiary plant fossils known from northern Africa. Phytogeographic comparison is also made with the Malaysian region. It is envisaged that there were large scale migrations and intermingling of floras over Malaysia, India, Arabia and Eastern Africa during Neogene time. Records of Dipterocarpaceae provide significant evidence. Water seems to have been a major factor in controlling the distribution of plants at low latitudes throughout the Cenozoic era.The palaeogeography of India during the Early Eocene and Miocene epochs has been reconstructed on the joint evidence of plant and animal fossils.Much work remains to be done before we shall have a clear understanding of the sources and migrations of the plants which have survived in southern Asia throughout Tertiary times to the present.

ISSN:0040-0262    

DOI:10.2307/1219280

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryProblems involved in the setting up of a systematic approach to the study of the geochemistry of landscapes for biogeochemical prospecting research in Canada have been described. Two aspects of the approach, 1) the establishment of a simple technique for the display of landscape geochemical data for purposes of comparison and 2) the setting up of a series of projects at different levels of detail needed to formalize the collection of information from landscapes for purposes of comparison, have been outlined and discussed by means of examples. Although the research described is at a relatively early stage of development it is believed that it is both feasible and practical to approach biogeochemical prospecting research along the lines described. It should be stressed that the aspects of the approach described here are essential preliminaries to detailed investigations involving comprehensive morphological, chemical and mathematical methods which together would provide basic information on the pattern and processes of the circulation of elements in landscapes including mineral deposits. Intensive investigations of this type are very costly in money, time and resources and would only be justified after very careful selection of sites along the lines described above.

ISSN:0040-0262    

DOI:10.2307/1219281

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe development of botany in the tropics falls into four periods: (i) the age of the pioneer botanical explorers, which extended into the 19th century, (ii) the age from then to the First World War in which the plant resources of the tropics were developed mainly by colonial governments, (iii) the period between the two World Wars when improved hygiene and transport opened up new possibilities for scientific work in tropical countries and (iv) the present period which began at the end of the Second World War, in which even greater facilities for botanical research in the tropics have been accompanied by a continually accelerating destruction of the tropical biota. The present is therefore the best moment there will ever be for studying tropical botany.

ISSN:0040-0262    

DOI:10.2307/1219282

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryTropical botanic gardens remain important for their records of local floras and as bases for continued monographic work. This work is still far from complete in the equatorial tropics, and it is the essential basis for all other study of plants, whether scientific or technological. The gardens also remain important as collections of living plants for botanical study of all kinds (especially for genetics and plant breeding) and for local education. A closer association of the gardens with universities is desirable, so that academic botanists may be fully aware of the range of local plants available for investigation. There is much still to be understood about the physiological adaptations of plants in the ever‐wet tropics, a subject hardly dealt with in text‐books of plant physiology published in temperate regions.

ISSN:0040-0262    

DOI:10.2307/1219283

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryChromosome counts indicate that x = 9 in the aquatic genusNymphoides(Menyanthaceae). New World species are tetraploid, but diploid species as well as tetraploid ones occur in the Old World. The pan‐tropicalN. indicais tetraploid in the New World and diploid in the Old World, but no consistent morphological characters have been found that separate these chromosomal races. The EurasianN. peltatais hexaploid. Self‐incompatible distyly, dioecism, and homostyly are present in the genus. The latter two breeding systems are believed to be derived from distyly. The ColombianN. flaccidaseemingly occurs in the long‐styled form only and because of its self‐incompatibility may reproduce exclusively by vegetative means.

ISSN:0040-0262    

DOI:10.2307/1219284

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThree taxa of the genusAbiesoccur in Eastern North America:A. balsamea(L.) Mill. var.balsamea, A. balsamea(L.) Mill. var.phanerolepisFern., and A.fraseri(Pursh) Poir. The occurrence of “intermediate” populations in the Mid‐Appalachians has resulted in a confused literature concerning the delimitation and distribution of these taxa. Data obtained from serological and electrophoretic investigation of seed protein are presented which support results of independent studies by Myers and Bormann (1963) and Robinson and Thor (1969). These data indicate thatA. b. var.balsameaandA. fraseriare closely related and recently segregated taxa and thatA. b. var.phanerolepisis more closely related toA. b. var.balsameathan toA. fraseriand is not of hybrid origin.

ISSN:0040-0262    

DOI:10.2307/1219285

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryJuniperus asheiBuch. was analyzed throughout its Texas distribution for areas of population differentiation and possible hybridization withJ. virginianaL. andJ. pinchotiiSudw. utilizing both morphological and chemical (terpenoid) characters. The volatile terpenoids of the foliage were analyzed by gas chromatography. Numerical methods included: analysis of variance; SNK tests; contour mapping of individual characters; differential systematics; and numerical taxonomy. Some peripheral populations ofJ. asheishow divergence of both terpenoid and morphological characters. This divergence is not, apparently, due to hybridization withJ. virginianaorJ. pinchotii. No evidence of hybridization was detected betweenJ. asheiandJ. virginianaorJ. pinchotii. Differential systematics and numerical taxonomy were found to be of considerable value in the analysis of infraspecific variation.

ISSN:0040-0262    

DOI:10.2307/1219286

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryRind and leaf oils of triploidCitrushybrids from 5 crosses, and their diploid and tetraploid parents, were analysed by gas chromatography. Two‐thirds of the chromosome complement of each hybrid was evidently contributed by the 4n parent. Overall, a wide range of percentages of the oil components occurred among hybrids and parents. There were differences significant at 1% in 80 of 90 parent‐hybrid group comparisons. There was no regular, dominating effect of the 4n parents, and in many cases the influence of 4n and 2n parents seemed about equal. However, among hybrids involving 4n lemon there was often a tendency for leaf oil levels to follow those of that 4n parent. The general absence of such an effect in the rind oils, and in the leaf oils of the other crosses, parallels the implication of an earlier study in which autotetraploids of several Citrus species were usually similar to their parental diploids, in their percentages of rind oil components.Where 2 or 3 sets of hybrids had a common parent, either 2n or 4n, there was also no constant effect of that parent, from set to set, as compared to other parents involved. Variation in the percentages of any specific oil component was great among the 6 sister triploids in many crosses. Individuals sometimes approached the level of one parent, and sometimes that of the other. Transgression of one or more hybrids beyond either parent frequently occurred, and was particularly prominent with decanal, linalool, and linalyl acetate. Percentages of components in the leaf were often different from those in the rind.It is clear that these polyploid hybrids of rather closely related species show many inherited differences in oil components. These differences are principally quantitative and probably reflect genetic recombinations which have altered intermediate biochemical pathways.

ISSN:0040-0262    

DOI:10.2307/1219287

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryFor a wider range of usefulness to buyers, merchants, breeders, and scientists, registers of cultivars should include the breeding history of each particular cultivar as far back as it can be traced. A cross reference of synonyms and translations of the cultivar names is also valuable.It is extremely laborious to find, select, interpret, record, and organize the pertinent information for such a register; compiling and updating the complete register is particularly tedious. This work can be greatly simplified through the use of an adequate computer system. This paper describes a system which has been developed for use with Oat cultivars (Avena) but which could be directly applicable in other areas as well. The system is completely automated throughout requiring only simple data input in the initial stages. Furthermore, the system is composed of several parts which can be used independently for specific purposes such as producing pedigree charts.A brief discussion concerning the benefits of such a register is also included.

ISSN:0040-0262    

DOI:10.2307/1219288

出版商:Wiley    

年代:2019

数据来源: WILEY