1. Diboll, A. G., and D. A. Larson: An electron microscopic study of the mature megagametophyte in Zea mays. Amer. J. Bot. 53, 391?402 (1966).
2. Eymé, J., et C. Suire: Au sujet de l'infrastructure des cellules de la region placentaire de Mnium cuspidatum Hedw. (Mousse bryale acrocarpe). C.R. Acad. Sci. (Paris) 265, 1788?1791 (1967).
3. Feder, N., and T. P. O'Brien: Plant microtechnique: some principles and new methods. Amer. J. Bot. 55, 123?144 (1968).
4. Gunning, B. E. S., and J. S. Pate: ?Transfer Cells? ? Plant cells with wall ingrowths, specialised in relation to short distance transport of solutes ? their occurrence, structure and development. Protoplasma (Wien) (in press).
5. Maier, K.: Wandlabyrinthe im Sporophyten von Polytrichum. Planta (Berl.) 77, 108?126 (1967).