. La microscopie électronique ; actes de la Conférence de Stockholm, septembre, 1956. La microscopie électronique. Certaines applications de la Botanique Technique Replica Carbone D. E. Bradley, Lahoratory Recherche Associated Electrical Industries Ltd., Aldermastoii, Berkshire il est probable qu'une connaissance de la sous-microstruc- ture du sporoderme serait d'une certaine valeur dans une étude de la flore post-glaciaire. La microscopie électronique de la structure de surface des grains de pollen a été rendu possible par l'utilisation de répliques de carbone : la technique a été appliquée pour la première fois dans ce domaine par Muhlethaler (4). Dans le présent travail, o

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. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. Some Botanical Applications of the Carbon Replica Technique D. E. Bradley Research Lahoratory, Associated Electrical Industries Ltd., Aldermastoii, Berkshire It is likely that a knowledge of the sub-microstruc- ture of the sporoderm would be of some value in a study of post-glacial flora. The electron microscopy of the surface structure of pollen grains has been made possible by the use of carbon replicas: the technique was first applied in this field by Muhlethaler (4). In the present work, over sixty different species were studied in order to ascertain firstly, the reliability of the replica method developed for the purpose, and secondly, the range of structures which might be encountered in a wide study of pollen. The replica method was identical with that described elsewhere (1), save for one modification. It was found more satisfactory to dust pollen onto the initial Formvar substrate and then disperse it with acetone or alcohol, rather than to suspend the grains in water and dry down a drop of the suspension. It was found that the efficiency of the technique depended on the size of the pollen grain. In the case of large grains, the method was only 10 % efficient, i.e. only 10 out of 100 grains were replicated, the remainder breaking up and leaving a hole in the replica film. It is, of course, only necessary to take micrographs from a few grains so that this 10% efficiency was found to be quite adequate. In the case of small grains, the efficiency was at least 50 ';'o. It was found that the use of acetone or alcohol to disperse the grains caused the absorption of suffi- cient moisture during the evaporation of the solvent to cause the expansion of some grains. Many pollen grains are deeply divided by grooves, and the swell- ing causes the grooves to be pushed outwards so that a grain in the form of an ovoid becomes a sphere. This is a well known phenomenon. It

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