Cell Differentiation

The reader of this volume will put it down at last convinced that there is such a phenomenon as differentiation. A vast number of examples are given, some in great detail. Differentiation processes in roots are described by Robert Brown, J. K. Heyes, J. H. Leech, H. H. Mollenhauer and W. G. Whaley, J. Torrey; C. H. R. Raven for mollusc eggs and J. Heslop-Harrison for floral organs; H. E. Street and G. G. Henshaw for suspension cultures of plant cells. We are, of course, accustomed to the alterations in cell shape and structure which accompany differentiation and which can be seen with a microscope. Today, these changes are pursued on the level of electron-microscopy and the article of Leech et al. includes some very fine electron-micrographs of different kinds of cells during the course of root development. Similar studies have been made by C.H. Waddington with Microasterias and others. Today also, it is fashionable to determine whether cellular content of particular proteins, or enzymatic activities, or even of metabolites, alters during the course of development.