The different layers that form an ovule of a seed plant have different evolutionary origins and anatomical meanings, and are generally homologous throughout the seed plants. But most people, when they first look at a sectioned ovule under a microscope, see a mass of cells that all look more or less alike. These tutorials enable you to highlight each layer, so that you can visualize them independently in the context of each ovule.
The tutorials require the Macromedia Flash plug-in. Each one has a micrograph of an ovule in longitudinal section, and a list of the layers, in order from the outside in. If you point with the mouse to the name of a layer, or to the layer itself, it will stand out from the background. There is no need to click on the names, but it won’t do any harm.