Electron microscopy is an important tool for studies of plant structure. Electron microscopes utilize focused electron beams rather than visible light and are capable of resolving or detecting much finer details than the light microscope. Two types of electron microscope have been used to study plant cells in culture, the transmission (TEM) and scanning (SEM) electron microscopes. With the TEM, the electron beam penetrates thin slices of biological material and permits the study of internal features of cells and organelles. The TEM has been particularly important for basic studies of the structure and function of plant cell organelles such as microtubules and coated vesicles, examining polyethylene glycol-induced fusion of protoplasts, and monitoring internal changes during the development of cultured explants (e.g., Fowke 1989;Fowke et al. 1985Fowke et al. , 1991. The electron beam of the SEM scans the surface of prepared specimens. Thus, the SEM is important for studying the external morphology of intact cells, tissues and organs and is capable of resolving details intermediate in size between those detected by the light microscope and the TEM.Specimen preparation for the TEM is much more complicated and time consuming than for the SEM. Both procedures require specimen fixation and dehydration, but TEM specimens must also be infiltrated and embedded in epoxy resins, a process usually requiring a number of days. The ultramicrotome must also be mastered in order to prepare thin sections for examination in the TEM. Specimens fixed and embedded for TEM can also be sectioned and stained for light microscopy. Such sections facilitate location and orientation of critical specimens for observation in the TEM. In addition, the sections provide excellent material for morphological studies by light microscopy. However, unlike the methacrylate sections described in Chapter 17 on botanical microtechnique, such sections are permeable to only a few aqueous stains and are not suitable for histochemical work.Extensive and detailed methods for ultrastructural work with plants have been published in the form of reviews and books (e.g., Weakley 1981;Robinson et al. 1987;Hall and Hawes 1991). Methods vary with different specimens and, therefore, it is not possible to present a single standard method for all cultured plant materials. The methods described below for both TEM and SEM have proved satisfactory with a variety of different specimens and should with minor modification be suitable for most situations.