division of the nucleus in the spore-mother cells of plants. The wax employed is made of a mixture of one part of white wax, with five parts of paraffin, the melting point of which is about 50° C. SATURDAY, SEPTEMBER, 14. The Section did not meet. MONDAY, SEPTEMBER 16. A joint discussion with Section B was held on the Relation of Agriculture to Science. See p. 660. The following Papers were read:— 1. On the Destruction of a Cedar Tree at Kew by Lightning. By W. T. THISELTON-DYER, F.R.S. The President of the Section exhibited photographs and specimens of a large cedar (Cedrus Deodara, Loud.) from Kew, which had been struck and completely shattered by lightning on August 10. It was pointed out that the main stem had been in part blown into matchwood by the violence of the shock, and branches were torn off with large portions of the trunk adhering to their base. The explosion seemed to have been centrifugal, the stem having been disrupted from the centre, and not merely stripped superficially. 2. On the Formation of Bacterial Colonies. By Professor Marshall Ward, F.R.S. The author has examined the details of development of the colony in numerous species from a single spore by employing microscopic plate-cultures, which can be kept under observation with a one-twelfth and even a one-twentieth oil-immersion lens, or by making pure Klatschpräparate on cover-slips covered with a thin film of gelatine. He finds many factors of importance affecting the form, extent, rapidity of growth, and other characters of colonies; the elasticity of the gelatine, the presence of moist films on the surface of the gelatine, the rate of (slight) liquefaction, &c., all being of importance in explaining the shapes, &c., of submerged colonies-whetstone shaped,' moruloid, spherical, or lobed colonies-the mode of emergence and spreading over the surface of the gelatine, the formation of radiating fringes, iridescent plates, &c. Exposure to light during the development of liquefying colonies may profoundly affect their shape and other properties, a phenomenon closely connected with the retardation of liquefaction and growth. Pigment bacteria may give rise to perfectly colourless races when cultivated under certain conditions, and the colour restored by again changing the conditions; a fact which the author has not only confirmed with red forms, but which he shows to be true of a violet bacillus. Species commonly described as non-motile show active movements under certain conditions, and the sizes of bacteria are not constant in different regions of one and the same colony. Details have been worked out for series of types the extremes of which differ considerably in liquefying power, and essential difference in the appearance of a colony may depend on the amount of liquefying power evinced. Some curious cases of travelling films, the lobes and contorted tresses of which move like amœbæ over the surface of the gelatine, were also examined. The facts point to (1) differences in colonies even of one species may depend on much more subtle differences in cultures than are usually recognised; (2) varietal differences may occur in two bacilli of the same species (isolated from a river), due to the different vicissitudes the two individuals have been subjected to during their sojourn in the water; (3) the difficulties met with in diagnosing species' of bacteria with the aid of works of known authority are partly due to varieties of the same species being recorded by different observers under different names, and the author thinks some more consistent prearranged plan of working out the characters of such forms should be developed by bacteriologists than at present exists. 3. On a Supposed Case of Symbiosis in Tetraplodon. By Professor F. E. WEISS. The author exhibited specimens of Tetraplodon from the Cuchullin Hills in Skye, where it was found plentifully on animal excreta. In September he found many of the patches mixed with an orange-coloured Peziza, which did not appear to have in any way injured the moss plants. The rhizoids of the moss, however, contained in many cases fungal hyphae closely resembling those of the Peziza, and though present in the cells of the moss these latter did not seem to be injured by them. He suggested that this might be a case of symbiosis; the moss, as in the case of other green plants, making use of the fungal hyphæ to obtain its nutriment from the organic material. The ultimate proof of such a case of symbiosis would, however, necessarily depend upon culture experiments, which he understood were now being made by another observer. TUESDAY, SEPTEMBER 17. The following Papers were read : 1. On Amber. By Dr. CONWENTZ, Danzig. The author of this paper gave an account of the Baltic and English amber, and their vegetable contents. After describing the different forms of Tertiary amber, he referred to the occurrence of succinite on the coasts of Essex, Suffolk, and Norfolk; the specimens are usually found with seaweed, thrown up by the tides. Occasionally pieces have been met with weighing over two pounds. Dr. Conwentz described the method of examining the plant fragments enclosed in amber, and compared the manner of preservation with that of recent plant sections mounted in Canada balsam. The amber was originally poured out from the roots, stems, and branches of injured or broken trees, in the form of resin, which on evaporation became thickened, and finally assumed the form of succinite or some similar substance. For the most part the fossil resin was derived from the stems and roots of coniferous trees of the genus Pinus. In addition to the exceptionally well-preserved tissues of coniferous trees, the Baltic amber has yielded remarkable specimens of monocotyledonous and dicotyledonous flowers. Some of the most striking examples were illustrated by means of the excellent coloured plates from Dr. Conwentz's monograph on the Baltic amber.1 1 Monographie der baltischen Bernɛteinbäume. Danzig, 1890 2. The Wealden Flora of England. By A. C. Seward. Mr. A. C. Seward, after referring to the various species described by Mantell, Carruthers, Starkie Gardner, and others, from the Wealden strata of England, briefly described a large number of plants from the British Museum collection. During the last few years Mr. Rufford, of Hastings, has obtained an extremely valuable and rich collection of plants from Ecclesbourne, Fairlight, and other localities; and these have now become the property of the nation. The following species are at present known from the Wealden of England; some of these have already been figured in the first volume of the catalogue of the Wealden flora, and the remainder are dealt with in the forthcoming second volume:--Algites valdensis, sp. nov., A. catenelloides, sp. nov., Chara Knowltoni, sp. nov., Marchantites Zeilleri, sp. nov., Equisetites Lyelli, Mant., E. Burchardti, Dunk., E. Yokoyama, sp. nov., Onychiopsis Mantelli (Brong.), O. elongata (Geyl.), Acrostichopteris Ruffordi, sp. nov., Matonidium Göpperti (Ett.), Protopteris Witteana, Schenk., Ruffordia Göpperti (Dunk.), Cladophlebis longipennis, sp. nov., C. Albertsi (Dunk.), C. Browniana (Dunk.), C. Dunker (Schimp.), Sphenopteris Fontainei, sp. nov., S. Fittoni, sp. nov., Weichselia Manteili (Brong.), Taniopteris Beyrichii (Schenk.), T. Dawsoni, sp. nov., Sagenopteris Mantelli (Dunk.), S. acutifolia, sp. nov., Microdictyon Dunkeri, Schenk., Dictyophyllum Römeri, Schenk., Leckenbya valdensis, gen. et sp. nov., Tempskya Schimperi, Cord., Cycadites Römeri, Schenk., C. Saporta, sp. nov., Dionites Dunkerianus (Göpp.), D. Brongniarti (Mant.), Nilssonia Schaumburgensis (Dunk.), Otozamites Klipsteinei (Dunk.), O. Göppertianus (Dunk.), Zamites Buchianus (Ett.), Zamites Carruthersi, sp. nov., Anomozamites Lyellianus (Dunk.), Cycadolepis, Carpolithes, Androstrobus Nathorsti, sp. nov., Conites elegans (Carr.), C. armatus, sp. nov., Bucklandia anomala (Stokes and Webb), Fittonia Ruffordi, sp. nov., Bennettites Saxbyanus (Brown), B. Gibsonianus, Carr., B. (Williamsonia) Carruthersi, sp. nov., Yatesia Morrisi, Carr., Withamia Saporta, gen. et sp. nov., Beckleria anomala, gen. et sp. nov., Dichopteris, sp., Sphenolepidium Kurrianum (Schenk.), S. Sternbergianum (Dunk.), Pagiophyllum crassifolium, Schenk., Brachyphyllum obesum (Heer), B. spinosum, sp. nov., Pinites Solmsi, sp. nov., P. Dunkeri (Carr.), P. Mantelli (Carr.), P. patens (Carr.), P. Carruthersi (Gard.), &c. 3. On the Diurnal Variation in the Amount of Diastase in Foliage Leaves. By Professor J. REYNOLDS GREEN, F.R.S. The diastase which is present in foliage leaves varies in amount during the day, being greatest in the early morning, and least after sunset. The variation has been ascertained to be chiefly, if not entirely, due to the action of the sunlight. The author showed last year, at the Oxford meeting, that diastatic extracts exposed to sunlight or electric light, without the interposition of any form of screen, had their activity largely impaired, the damage amounting sometimes to 70 per cent. Experiments made upon the living leat of a scarlet-runner showed a similar destructive action of the light, the amount of destruction only amounting, however, to about 10 to 20 per cent. The author attributes the difference to the screening action of the proteids in the cells of the leaf. 4. On the Structure of Bacterial Cells. By HAROLD WAGER. In this paper an account was given of the present state of our knowledge of the cells of bacteria. Reference was made to the observations of Schottelius, Migula, De Bary, Bütschli, and others. The author showed that it is possible to demonstrate in the majority of bacterial cells the presence of two substances, one of which may be regarded as protoplasmic in nature, and a second which stains deeply when acted upon by fuchsin and kindred staining substances, and which may be regarded as nuclear. It was pointed out that this nuclear substance does not possess the structure of nuclei in the cells of higher plants. 5. On the Prothallus and Embryo of Danæa. By G. BREBNER. Mr. Brebner gave an account of the prothallus and sexual organs of Dan ea simplicifolia, Rudge, as the result of investigations made on some material from the Botanic Gardens in British Guiana. He pointed out that there is a close similarity between Danaa and the other two genera of the Marattiacea, Angiopteris and Marattia, of which the prothallus has been previously described. An interesting fact was noted as regards the prothallus rhizoids, which possess a distinctly septate structure, and so far resemble a moss protonema. Possibly imilar septate rhizoids may be found in the other marattiaceous genera. The development of the antheridia of Danea agrees in the main with that in Marattia and Angiopteris: the material did not allow of any developmental study of the archegonia. The concentric bundle of the primary embryonic stem shows an endodermal layer. On the whole the author found in Danæa a complete agreement, in all essential features, with Angiopteris and Marattia, as regards prothallus, reproductive organs, and embryo development. 6. On Cross and Self Fertilisation, with special reference to The time has passed for regarding self-fertilisation as being always necessarily harmful in itself, and it is now recognised as a regular feature in the life-history of many plants. There exist many cases of plants in which both self and cross pollination occur nearly, or quite, simultaneously, and it is very desirable to know what happens in these cases. Darwin's experiments render it probable that prepotency of foreign pollen is usual. The author's experiments have been devoted to a study of the relative chemical attraction of own' and 'foreign' pollen by the same stigma (chiefly in gelatine and agar cultures), and have given negative results. It seems probable, putting together all the various known facts, that prepotency, where it occurs, is due to actions set up after the pollen tubes have entered the stigma, these actions tending to favour the growth of the 'foreign' pollen-tubes, and to check that of the 'own' pollen. |