The overtopping, reduction and syngenesis have combined to produce a synangium of psilotum fig. Frontiers the evolution, morphology, and development of. Apospory and apogamy in pteridophytes biology discussion. Morphologists have long been concerned with the fundamental nature of the vascular plant bodywith the relationships between root, stem and leaf, and with the origin of reproductive structures. The leaves that bear sporangia are known as sporophylls. The evidence pinpoints testable developmental and genetic hypotheses relating to the origin of branching and indeterminate shoot architectures prior to the evolution of leaves, and demonstrates underestimation of polyphyly in the evolution of leaves from branching forms in telome theory hypotheses of leaf evolution. Finally, conglomerate mergers are revised under the portfolio theory of merger effects. A seed may be defined as an integumented surrounded by integument and indehiscent not ruptured o. The true story seems to be lost in antiquity and perhaps will never.
The telome theory can be applied to interpret the evolution of a synangium of psilotum. The telome is the fundamental supercellular building block in plants. According to telome theory the earliest levees are flattened telomes or phylloids, and the sporangium in all cases, together with its stalk or sporangiophore, is a fertile telome. In the case of leaves, zimmermann essentially envisaged the transformation of a stem into a. The vegetative plant body is a sporophyte in pteridophytes. Among living plants, this type of stele is found only in the stems of ferns. These processes may have occurred in various sequences in different groups of vascular plants.
Stelar evolution in pteridophytes ppt by easybiologyclass. The distinction between main stems and strongly branched lateral stems evident in species such as p. Grypania is an early, tubeshaped fossil from the proterozoic. Stellar organization and evolution of stele in pteridophytes. Occurrence and evolution of pteridophytes biology boom. Zimmermanns telome theory of megaphyll leaf evolution. In a vascular plant, the stele is the central part of the root or stem containing the tissues derived. This is commonly interpreted in terms of the more highly specialized leaves of the leptosporangiate ferns as corn.
Apospory is the development of unusual diploid gametophyte from the vegetative parts of sporophyte and not from the spores. Using the telome mesome distinction, and the concept of universal elementary processes underlying the change in form in all plants, the theory was an ambitious synthesis based on the proposition that evolutionary change might be understood by a simple set of developmental or evolutionary rules. Merits and demerits of telome theory biology 840 words. Tomescu, 2009 rely heavily on data from fossils, and the. The early devonian rhynie chert flora, dominated by rootless, leafless rhyniophytes with dichotomously branched stems and terminal sporangia, led to the telome theory of vascular plant morphology 141, which subsumed the classical theory that the sporophyte consists of stems, leaves, and roots by postulating that leaves p1. The stele is a real entity and present universally in all axis of higher plants. Buy isbn9781403930309 at 16% discount by macmillian india ltdnew delhi. Apogamy is the development of an unusual haploid sporophyte from the gametophyte without the fusion of gametes. Classification of pteridophytes smith, 1955, sporne 1975 2. While the widespread use of mergers and acquisitions in practice. On leafarchitecture as illuminated by a study of the pteridophyta. In contrast, apogamy is the development of 1n sporophytes without gametes and syngamy from vegetative cells of the gametophyte.
Welfare concerns arrive when the merging firms produce complementary. The origin and evolution of leaves in vascular plants has been widely debated. The 2 n aposporous gametophytes and the 1 n apogamous sporophytes are usually infertile under natural conditions because of disruption of cytological events. The complex venation of the megaphyll leaf product was thus seen as an evolutionary fusion and planation product of a number of protostelic axes fig. The concept of the stele was developed in the late 19th century by french botanists p. Compound sporangiophores, like those of equisetum, are syntelomes. Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid.
Diversity of microbes and cryptogams bryophyta geeta asthana department of botany. Followers of the telome theory believe that in a telome truss, of the two telomes the upper was fertile and the lower sterile. At first you see forms vaguely resembling ferns and bit by bit the image becomes sharper. Pteridophyta teridafata os made from two greek roots that mean winged pteryz.
Usually a fern is defined as a cryptogam with sporangia evolving from the leaf. The origin and early evolution of vascular plant shoots. This interpretation, which was formalized as the telome theory by walter zimmermann 1930, has been the prevailing view of the evolutionary origin of megaphyllous organs. Figure 4 three processes from the telome theory proposed to be involved in megaphyll evolution redrawn from zimmermann, 1952.
Jeffrey 1898, for the first time pointed out the stelar theory from the point of view of the phylogeny. Journal of economic education 19692015 books by language journal of autism and developmental disorders 19712014 journal of paediatric dentistry. Leaves are lateral determinate structures formed in a predictable sequence phyllotaxy on the flanks of an indeterminate shoot apical meristem. Content is available under the creative commons attribution share.
Evolution and biogeography of gymnosperms request pdf. The organism could have been a giant bacterium or bacterial colony, but because of its size over one centimeter and consistent form, is more likely to have been a eukaryotic alga. I thought it would be a good idea to put these 3 questions together because they all deal with. This type is found in primitive fossils and living ferns. Being the main conspicuous organ of nearly all vascular plants and often easy to recognize as such, it seems surprising that leaves have had multiple origins. The theory that the leaves megaphylls of ferns and seed plants evolved by the modification of terminal branches telomes of stems. It envisages that firstly, instead of the primitive equal dichotomous branching of the stem, there developed a main axis with lateral side branches. Seed habit is an evolutionary trend in vascular plants where naked megasporangium got covered by a vascular integument and hence a seed was formed. I the emergence of ferns is best to be compared with a looming up from the fog.
Pteridophytes or pteridophyta, in the broad interpretation of the term or sensu lato, are vascular plants plants with xylem and phloem that reproduce and disperse via spores. Pteridophytes, gymnosperms and paleobotany 6 4 3 25 75 100 core paperiii practicali covering theory papers i and ii 8 4 4 40 60 100 elective i microbiology or evolution 4 3 3 25 75 100 electrive ii plant research methodology or ethno botany 4. The reference is to the winglike appearance of the compound leaves fronds that are characteristic of most ferns. According to telome theory, the sporophylls originated by the modification of telomes in a telome truss.
In its general form, the telome theory proposes that, by combining and modifying simple multicellular telomes through one or more developmental processes, it is possible to explain all extant and extinct plant morphologies. Natural apogamy is common in ferns like dryopteris, adiantum, osmunda, pteris etc. The telome theory offers one explanation for the nature of the aerial. In common with all groups of multicellular algae they have a life cycle which involves alternation of generations. How do you determine if a molecule is polar or nonpolar. The sporophylls of lycopsids always have a single sporangium borne on their adaxial surface surface close to the axis. In some pteridophytes the sporangia develop on stems i.
This content was copied from view the original, and get the alreadycompleted solution here. The degree of master of science in plant science aims to introduce the students to various aspects of plant biology. The sporophytes reproduce by spores which are produced within sporangia. Stelar theory, components of stele, different types of steles in plants, protostele.
The spatial arrangement of vascular bundles and the theory of steles. Evolution of sporophytes in pteridophytes telome theory. Today, merger research has developed into a voluminous subfield of strategic management. This page was last modified on 26 december 2014, at 03. The phylloids are the prototypes of the microphyllous foliage leaves. The telome concept has been used in understanding the origin and evolution of the following major groups of plants. Different types of steles in pteridophytes and its evolution in higher plants.
American journal of botany botanical society of america. Botany syllabus as per credit system the credit system pattern syllabus in affiliated colleges of university of pune will be implemented from the academic year 202014. In certain pteridophytes the sporangia are produced within specialized structure, the sporocarps e. The telome theory proposes instead that both microphylls and megaphylls originated by the reduction. Developmental details not to be included azolla, marsilea, equeisetum. Mbo02 june examination 2016 msc previous botany examination pteridophytes, gymnosperms and paleobotany paper mbo02 time. For example, broadranging and influential hypotheses of landplant evolution such as the telome theory zimmermann, 1952. The reproduction of efficiency theory semantic scholar. At the end of the course, the students are expected to have good working knowledge in the field of plant science. While in the pteridophytes, the main plant body is the sporophyte. The sporangium in all pteridophytes is initiated by the laying down of a crosswall in a superficial cell or a group of cells. There are actually three questions here, all dealing with rhynia rhynia is known by two names, the diploid life cycle rhynia major, and the haploid life cycle rhynia gwynnevaughanii.
572 260 1030 1112 1241 249 54 569 691 880 738 160 1013 413 1167 1211 1376 641 1305 570 372 1371 630 1143 1139 1047 1282 628 253 797 22 630 908 810 420 758 519 1323 64 357 562 304 779 1400