The Nikon MicroscopyU confocal microscopy image gallery was created with a PCM-2000 confocal scanning system interfaced to a Nikon Eclipse E600 upright microscope. Images were recorded in successive z-axis serial sections with C-Imaging Systems software with excitation illumination provided by an argon-ion and/or a helium-neon laser.

	Interactive Java Tutorial
ATTENTION Our servers have detected that your web browser does not have the Java Virtual Machine installed or it is not functioning properly. Please install this software in order to view our interactive Java tutorials. Visitors using the Netscape and Microsoft Internet Explorer browsers can download the appropriate software from the websites where the browsers are distributed. Please do not contact us for information about specific URLs where this software can be obtained.

Back to the first confocal sequence of club moss.

Allies to the true ferns, the club mosses and spike mosses are ancient plants distributed widely, throughout the tropics and temperate zones. One genus, Selaginella, represented by more than 700 species of small and delicate plants, is characterized by having a single, cup-shaped chloroplast per leaf and ligules, small tongue-like structures on the top of each leaf (near that base) with undetermined function.

Like other members of the division Lycophyta, the spike mosses have an asexual reproductive structure, the strobilus. Selaginella strobilus, commonly used in slide preparations, is scientifically named for this characteristic structure, which is spike-like. Strobili (plural of strobilus) form at the uppermost portion of fertile branches and are composed of sporophylls bearing a single sporangum. All species in the genus Selaginella are heterosporous; that is, they make two different types of reproductive spores. Megasporangia and microsporangia are produced in the same strobilus with spore mother cells present in both. They each divide by meiosis to produce megaspores and microspores, respectively. Megaspores develop into megagametophytes or females while microspores grow into microgametophyte or male plants. Fertilization of the megagametophyte takes place when the microgametophytes release their biflagellated sperm and they swim to reach the eggs during a rain shower or in a thin film of dew.

Sporophytes, the dominant phase in the club moss life cycle may come in three different growth forms: shrubby, erect, or mounds. They have adventitious roots, and the leaves (microphylls) are usually arranged in four vertical rows on a stem. The embryonic sporophyte is attached to the female gametophyte until mature and it establishes an independent existence.

Although living representatives of these ancient plants are of little commercial value today, the spike mosses are responsible for providing the biomass for most of our coal reserves. Some spike mosses are raised in greenhouses for use as ornamental plants. Their fossil ancestors first arrived about 410 million years ago and became dominant during the Carboniferous period (360-290 million years ago) as large (up to 40 meters) tree-like plants. These tree-like lycophytes died out during a Permian glaciation and tropical drought (around 250 million years ago), leaving only the herbaceous forms that survive today.