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Fagerland 1906 1919 1924 1935 1936 1947 2000
@Biology With Muhammad Sajid #biologywithmuhammadsajid botany zoology microbiology pathology mycology molecular biology Biochemistry and genetics Biology With Muhammad Sajid for FSc A-level BS and MSc Student's The angiosperms appeared suddenly in Cretaceous age about 65 million years back. Charles Darwin described this sudden appearance of angiosperms in lower or upper Cretaceous as an ‘abominable mystery. When angiosperms appeared for the first time in lower or upper Cretaceous, they were full fledged like the trees and the herbs of today. In support of this view Prof. Knowlton advocates in his ‘Plant of the past’, “from the time of their appearance they did not progress at all due to their full-fledged appearance in the Cretaceous”. The fossil records of the angiosperms also support their appearance full-fledged in lower or upper Cretaceous. The fossils of that age are so characteristic and modem in appearance that most of them can be referred unmistakably to living families, general and even to some species. Prof. Knowlton stated in his book, ‘Plant of the past’ “if a student of present day trees and shrubs, could have wandered over the hills and vales in those days, he would have found himself quite at home among the trees and shrubs growing there”. The forms of cycads and conifers, which long dominated the universe were already pushed background and the earth had become infact the earth of flowering plants. Charles Darwin has called this sudden appearance of angiosperms as an “abominable mystery”. However, some workers do not agree with the doctrine of ‘abominable mystery’. According to H.H. Thomas (1936), the angiosperms of the past replaced many of older gymnosperms in asturine and marshy waters. Graud Eury (1906) believes that the angiosperms came into existence through mutation. Guppy (1919) however, supported the view of mutation. Prof. Bertrand is of opinion that all the great groups of vascular plants (Pteridophyta, Gymnospermae and Angiosperms) not only arose quite independently of each other but also they originated simultaneously as far back in the Archian period (2000 million years old-oldest). There is a very considerable but scattered literature on the origin and phylogeny of angiosperms. The palaeobotanical evidence shows that there seems three possibilities as regards the origin of angiosperms. These possibilities are: 1. That the angiosperms are monophyletic in their origin but have had a very much longer history than at present known, perhaps stretching back into Palaeozoic times and with a whole series of missing links; 2. That the angiosperms are monophyletic but that the first and at present unknown group diverged quickly in terms of geological time, into a considerable number of different groups; 3. That the angiosperms are polyphyletic. According to Campbell, “both comparative morphology and the geological record indicate that the existing angiosperms represent a number of distinct phyla which cannot be traced back to a single ancestral type”. This statement shows that he does not believe in monophyletic origin of angiosperms. of Ranales with spirally arranged male and female sporophylls and the cone of Cycadeoidea are definitely alike. Both the groups were also abundant in the Cretaceous 2. Coniferae-Amentiferae Theory: Engler and Prantl (1924) rejected the Cycadeoidean origin of angiosperms, as proposed by Hallier (1906) earlier. They held the view that dicotyledons and monocotyledons had arisen independently from a hypothetical group of extinct gymnosperms (allied coniferae) with unisexual strobilus which developed in the Mesozoic. Thus, according to them, the angiosperms had a polyphyletic origin, and evolution took place on several parallel lines from the beginning. They considered the monocotyledons to be more primitive than the dicotyledons. The unisexual naked (without perianth) condition of the angiospermic flowers, such as Pandanales (monocotyledons) and Amentiferae (catkin-bearing dicotyledons, e.g., Casuarina. Salix, Betula, etc.) was most primitive. But according to the modem classification these orders are regarded more advanced. 3. Gnetales-Casuarinales Theory: Wettstein (1935) held the view that angiosperms of Casuarina type evolved from Gnetales, (particularly Ephedra), a highly advanced group of gymnosperms, which branched off from the main gymnospermic line. However, there are some angiospermic features in Gnetales but this group has meagre fossil records, and not gone earlier than Tertiary. Fagerland (1947) was of the opinion that both Gnetales and Proangiosperms had a common ancestor and the modern angiosperms evolved from the Proangiosperms in Polyphyletic lines
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