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Illustrations of these fossils as well as their descriptions have been critically studied. None of them shows all the anatomical characteristics similar to those of the fossil from the Garo Hills. Dipterocarpoxylon gopperti, Kräusel, (23) shows some slight resemblance to the fossil in the cross section but the tangential sections are entirely different. Again, Dryobalanoxylon spectabile, Den Berger, (9) and this fossil show some agreement in their tangential view but their cross sections are not at all similar. In view of these facts it can, therefore, be concluded that the fossil from Garo Hills has no affinity with any of the Dipterocarpoxyla previously reported from outside India.
(4) Name and diagnosis. A comparative study of the fossil G. S. I. Type No. 16502 with the living dicotyledons has shown its greatest affinity to the genus Anisoptera. Considering our imperfect knowledge of the anatomy of the living Dipterocarpaceae it does not at present appear to be judicious to give it that generic name. The fossil from the Garo Hills is, therefore, named Dipterocarpoxylon garoense, which means that it belongs to the order Dipterocarpaceae excluding the genera Monotes and Marquesia. Its specific diagnosis is given below :
Dipterocarpoxylon garoense, sp. nov.*
the eye, medium-sized to rather large ; tangential diameter of solitary vessels 169 +94, radial diameter 268 +8y, more or less evenly distributed, usually 112 (138) single or groups per 25 mm. sq., in groups of 2-4 (7), 30 per cent. in pairs and the rest single ; tylosed, occasionally filled with solid contents ; perforation plate simple, horizontal or oblique ; vessel elements with or without tail. Inter-vessel pit pairs fairly large, alternate, outline of border oval; aperture lenticular, horizontal or slightly oblique. Vessel-tracheid pits similar to inter-vessel pits. Vesselray pits two types : (1) one to a ray cell, usually large, (2) several to a ray cell, somewhat similar to inter-vessel pits but smaller, out
* Description of the fossil given here is in accordance with the standard method of describing a wood by Chattaway (4), Rendle and Clarke (31). Figures included in the description are based on counts as given below :-Vessel distribution 20 counts; tangential and radial diameter of vessels, 100); fibre
length, 50; ray distribution, 25;ray width and height, 50,
line of the border small, round to oval, aperture oval to lenticular. Vessel-parenchyma pits similar to vessel-ray pits.
Tracheids.- Vasicentric in a single row, occasionally intercepted by parenchyma cells. Pits exactly like vessel, their size and shape depending on the adjacent cells.
Fibres.-Thick to very thick-walled, irregularly arranged, showing no definite alignment in cross section, occasionally filled with solid contents. Septate fibres not observed. Inter-fibre pits simple to bordered, outline of border round to oval, aperture slitlike. Fibres short, 978+56u in length.
Parenchyma.-Not visible to the eye or with a hand lens, scanty to fairly abundant under microscope ; (1) paratracheal in rows of 1-3 (mostly 2) intercepted by tracheids; (2) metatracheal irregular, in narrow or wide bands, occasionally surrounding gum ducts; (3) diffuse, rather scanty. Inter-parenchyma pits round to oval, small to large, one to many per cell.
Rays.--Visible to the eye, moderately numerous, 5 per mm., heterogeneous, occasionally containing solid deposit; moderately broad to broad, 5-8 cells, 98–234 in width ; height usually more than 15 cells, very low to low, 720+144! ; uniseriate rays and outer cells of the multiseriate rays squarish to oblong vertically; the inner cells procumbent, irregularly arranged. The rays occasionally vertically fused, running to considerable height. Pits between ray cells small, numerous, oval or nearly so.
Gum ducts.-Vertical gum ducts noticed. (1) Diffuse or scattered in groups of 2-3, (2) in tangential bands of considerable length.
5. General remarks. Much has been written on the difficulty of identifying palæobotanical specimens based on isolated material. But it is doubtful whether one can always obtain complete material of foliar and reproductive remains to be sure of the specific naming of a fossil. In view of the progress made in plant anatomy within the last 50 years and of the certainty with which the isolated wood samples of the living species are now being identified in various laboratories, it appears to be possible to trace specimens of fossil wood to at least a genus or group of genera. According to this school of botanists the degree of certainty in the identification of a fossil wood will depend on the extent of our knowledge in the anatomy
of the family concerned. The order Dipterocarpaceae shows distinct anatomical characteristics by which its members can be easily distinguished from those of the others. Fossil woods possessing no gum ducts or only doubtful ones have in some cases been placed under Dipterocar poxylon. Such rash identifications have caused only confusion, as can be seen from the past record. All anatomical details of a fossil wood must match with those of the Dipterocarpaceae before it can be placed with certainty under Dipterocarpoxylon.
The present distribution of the Dipterocarpaceae has been recorded by various systematic botanists and this question has been fully discussed by Bancroft (1) in her paper on “A contribution to the Geological History of the Dipterocarpaceae ”. Lately, Kanjilal and Das (19) have published a 'Flora of Assam ’according to which only three genera, namely Shorea, Dipterocarpus and Vatica, occur in Assam. No mention is made by these authors of the genus Anisoptera, to which the fossil under investigation shows the greatest affinities. At present the Anisopteras are known to occur in Burma, Siam, Indo-China, Malay Archipelago and Philippine Islands, and the reason for their migration from western Assam is not well understood.
Dr. Fox's specimen from the Garo Hills is of great interest from the botanical point of view, for amongst the fossil woods so far reported from India, this alone shows in full detail the anatomical structure of the living Dipterocarpaceae and therefore would appear to be the first Dipterocarpoxylon to be recorded from India. From other countries, such as the Malay Archipelago and East Africa, a good many Dipterocarpoxyla have been reported. It was thought that a consideration of the age of these fossils from outside India might throw some light on the exact age of the fossil under investigation, but unfortunately no helpful clue could be obtained, for the Dipterocarpoxyla from outside India had been recorded from the Tertiary to the Recent and this is little more than what is already known about the age of the fossil in question.
(B) SPECIMEN G. S. I. No. K40/485.
(1) Description. To start with it may be mentioned here that the preservation of this specimen has been so bad that its detailed anatomical study was not possible. Whatever minute anatomy has been observed is recorded below :
Growth rings are very difficult to distinguish. There is some suggestion of a tangential parenchyma band which cannot with certainty be taken for a demarcation of growth ring (Pl. 16, fig. 4). Moreover, the specimen is so small that it does not show more than one such band. Vessels are more or less evenly distributed. Some are in radial pairs but majority are single. In shape they are oval to circular (Pl. 16, figs. 4, 6). Wood fibres are arranged in somewhat radial rows. Their walls are thin to fairly thick (Pl. 16, fig. 6). Parenchyma cells are difficult to distinguish from the wood fibres. There appear to be some round the vessels but the patterns they form are not at all distinct. Rays are not prominent either to the eye or with a hand lens but they are fairly distinct under a high power microscope. They are more or less uniformly distributed, 2 to 3 seriate, heterogeneous and low in height (Pl. 16, fig. 5).
(2) Name and diagnosis. The above anatomical data are too incomplete for any profitable comparison either with the woods of the living dicotyledons or with the dicotyledonous fossil woods that have so far been reported. In these circumstances it seems advisable to place it in the form genus Dryoxylon, Schleiden, and its diagnosis is given below :-
Specimen G. S. I, No. K40/485. DRYOXYLON Sp.
Vessels.-Medium sized to fairly large, visible to the eye ; solitary or in radial pairs of 2-3 (mostly 2); tyloses not observed ; perforation plate simple.
Wood fibres.-Thin to moderately thick walled, arranged in somewhat radial rows.
Parenchyma.—Distribution mostly indistinct; appears to be round the vessels and also in tangential bands.
Rays : Visible under high power of microscope, 2-3 seriate, heterogeneous and low in height.
1. Two dicotyledonous fossil woods from the Garo Hills of Assam are described and recorded.
2. The specimen G. S. I. Type No. 16502 has been intensively studied and its affinities to the living Anisopteras of Dipterocarpaceae are shown. Comparison of the fossil with those previously recorded from India and outside India is made and their possible affinities are discussed. G. S. I. Type No. 16502 appears to be the first specimen of Dipterocarpoxylon to be found in India and it is named as D. garoense.
3. Previous workers record occurrences of Dipterocar poxylon from Tertiary to Recent age. So the age of D. garoense is in agreement with their findings. Moreover, palæontological investigation of the beds in which D. garoense has been found, does not show any disagreement.
4. The specimen did not allow any detailed study, due to its bad preservation. Its anatomical details, as far as it has been possible to observe, are recorded.
Grateful acknowledgments are due to the Director and Dr. C. S. Fox of the Geological Survey of India for giving the author an opportunity to study these fossil woods. Thanks are also due to Prof. B. Sahni and Dr. K. M. Gupta of Lucknow University for allowing the author to examine the slides of Dipterocarpoxylon holdeni Gupta.