1,720,966 research outputs found
Suggestions for the classification and nomenclature of fossil spores and pollen grains
No full textAt many places in the present view the author has used, rather loosely, the convenient word "spore" to denote any one of the three categories of grain, viz., spore, prepollen and pollen, merely because of the lack of any suitable word which could be used instead. The special types of spores met with in the algae and the fungi have not been considered
Indelible clues to stomatal development in mature epidermis of plants
No full textThis article does not have an abstract
The lower Gondwana gymnosperms and their relationships
No full textGymnospermous remains in Lower Gondwanas consist of petrified woods, leaves and fructifications. While some woods may belong to Glossopteridales, the affinities of others are uncertain. Most of the Lower Gondwana leaves, unlike their contemporaneous northern counterparts, are simple. Among them one can recognize at least three definite alliances, viz. Glossopteridales, Noeggerathiopsidales and Coniferopsida. The unique leaf attached fructifications of the Glossopteridales may suggest some affinity with the pteridosperms. The leaves of Noeggerathiopsis (Noeggerathiopsidales) are Cordaites-like but no typical associated cordaitean stems and fructifications have been found. Among the Coniferopsida the lack of a female cone in Buriadia may suggest a very primitive conifer. Some other forms like Walkomiella, Searsolia and Paranocladus also appear to be coniferopsid. There are also some Incertae like Caulophyllites, Cheirophyllum, Dunedoonia and Psygmophyllum whose precise affinities are unknown. Detached sporangia and seeds occurring in the Lower Gondwanas not only confirm the existence of the three groups of gymnosperms suggested by other megafossils but they also indicate that they may have been more diverse
Structure and ontogeny of stomata in some Piperaceae
No full textThis article does not have an abstract
On the possible occurrence of anisospory in some Hepaticae
No full textPossible anisospory is reported for the first time in four species of Hepaticae, viz., Targionia indica Udar, Targionia hypophylla L., Cyathodium aureo-nitens Griff. (Mitt.), Cyathodium barodae Chavan. The report is based on observations of wide variations in size of spores comparable with those of anisosporous mosses of the family Orthotrichacae
Morphological studies in Argyreia Lour. (Convolvulaceae)
No full textA detailed anatomical study of two species of Argyreia, viz. A. nervosa Bojer and A. roxburghii Choisy, has been made. The structure of the cotyledonary and other nodes and internodes, including the developmental anatomy of the dominant axillary and accessory branches, the course and structure of medullary bundles, and the formation of successive rings of cambia along with the xylem and phloem, have been worked out. Two hitherto unknown types of saccate tracheidal and vessel elements are described. In the light of this work certain inaccuracies in observations and interpretations of some earlier workers are also corrected
On some megaspores from the triassic of Nidhpuri, India
No full textThe paper describes structural features of megaspores from the Middle Gondwana (Middle Triassic) beds of Nidhpuri. These include two species of Srivastavaesporites Bharadwaj et Tiwari viz. S. triassicus sp. nov. and S. major sp. nov.; Grambastisporites nidhpurensis gen. et sp. nov.; Trikonia emarginata gen. et sp. nov.; one species of Mamillaespora Pant et Srivastava, M. sidhiensis sp. nov.; Nidhitriletes spinosa gen. et sp. nov
Epidermal structure and stomatal ontogeny in some Celastraceae
No full textLeaves of Celastrus paniculatus, C. stylosus, Elaeodendron glaucum, Euonymus japonicus and E. pendulus are essentially hypostomatic, although a few stomata were observed near veins in the upper epidermis of Celastrus paniculatus. Their irregularly orientated stomata show guard cells partly underarched and partly surrounded by a ring of three to eight subsidiary cells. Surface walls of epidermal cells in Euonvmus pendulus show pits whose impressions are also seen in the cuticle. Rehfous (1914) had suggested that the sunken subsidiary cells of Celastrus europaeus, Catha edulis and Euonymus japonicus and four other species of the genus are formed in an unusual manner from segments of the guard cells. Our studies on the contrary indicate that the subsidiary cells in all our plants, including E. japonicus, are typically perigene. Mesophyll of all leaves is armed but the form of midrib bundles varies in different species and to some extent in different regions of the same leaf
Ontogeny of stomata in some Gentianaceae
No full textThe mature epidermis and development of stomata in some species of Gentianaceae, viz. Canscora deccusata, C. diffusa, Hoppea dichotoma, Enicostema littorale, Nymphoides cristatum and Gentiana pedicellata, are described. The stomatal development is shown to be trilabrate mesogenous in Canscora deccusata, C. diffusa, Enicostema littorale and Hoppea dichotoma, mesoperigenous in Gentiana and perigenous in Nymphoides. It is suggested that adoption of an aquatic habit by Nymphoides may have resulted in suppression of divisions in its perigenous stomata
The biogeography of the late Paleozoic floras of India
No full textThis paper reviews the biogeography of Paleozoic floras in India and addresses some of the important biogeographic questions that have been raised regarding the distribution of floras and faunas on the subcontinent. Little is known about the Silurian and Devonian floras. Plants of this age have been reported sparingly from the extra-peninsular Panjab-Kashmir Himalaya region. On the basis of the available evidence, land plants comprised a cosmopolitan world flora until the end of the Early Carboniferous. The beds above the Lower Carboniferous strata of Gondwanaland record a sudden large-scale extinction of plants due to widespread glaciation. The Gondwana glaciation is believed to have ranged from the Upper Carboniferous to the Upper Permian in different parts of the supercontinent. The earliest post-glacial fossiliferous strata of Upper Carboniferous/Lower Permian age in India are found in the Talchir Series which has been divided into two stages, the Talchir and the Karharbari. Talchir floras are depauperate and appear to have lived under unfavorably cold conditions. Approximately 20 Talchir taxa are reported. The floras are dominated by Gangamopteris. Conditions during the Karharbari in peninsular India favoured the development of diverse floras and extensive, thick peat accumulations. On the basis of floral evidence, climatic conditions are interpreted to have been milder and warmer than during the Talchir Stage. Gangamopteris still dominated but other glossopterids were becoming abundant and the pre-conifers first emerged. The Talchir series is overlain by the Damuda Series. The time during which the Damuda strata were being deposited is divided into three stages, the Barakar, Barren Measures (Kulti or Ironstone Shales), and the Raniganj. These stages are characterized by the increased diversification of Glossopteris and the waning of Gangamopteris. The tectonic movement of Gondwanaland northward away from its southern polar position resulted in gradually ameliorating temperatures during the Permian period. By the beginning of the Triassic, northward plate movement had positioned the subcontinent within an arid realm. Except for some rare occurrences of Glossopteris and Sphenophyllum, the glossopterids became extinct by the Triassic and were replaced by the Dicroidium floras. Some of the important biogeographic problems relating to the distribution of the late Paleozoic floras of India are concerned with the location of the northern, northeastern, and northwestern boundaries of Gondwanaland. The occurrence of non-Gondwanan forms at these localities could be interpreted as an indication that paleoecotones developed in the border areas between biogeographic provinces. However, an alternative hypothesis suggests that the areas of mixed floras constitute evidence that a microcontinent lay between the Eurasian plate and Gondwanaland. The occurrence of marine strata in the middle peri-Tethys region in the Salt Range and the Himalayan localities in Kashmir has long been established. However, the discovery of shelled faunas and smooth-walled acritarchs interpreted to be of marine origin throughout peninsular India indicates that the possibility of widespread marine transgressions into Lower Gondwana strata situated far from the Tethys will have to be considered
- …
