Stidd, Benton M. Department of Biological Science, Western Illinois University, Macomb, Illinois.
- Additional Reading
An order (class Polypodiopsida) of primitive ferns that consists of about seven living genera and 150 species. They exist mostly in tropical regions. These large, coarse, sappy ferns usually have large, highly divided fronds. Danaea simplicafolia, however, has an undivided frond consisting of a single blade. Stems of living genera (Angiopteris, illus. a; Marattia) are short and bulbous, often a foot or more in diameter. Other genera have smaller, mostly horizontal, and somewhat more elongated stems. The internal vascular system (food and water conduction tissue) of the stems and fronds can be quite complex, apparently as a function of size. Marattialeans are included among the primitive ferns primarily because of the way that the sporangia (spore-bearing organs) arise from a mass of cells rather than from a single cell as in more highly evolved ferns. Sporangia are generally fused together into a synangium. Synangia are borne on the lower surface of the pinnules and are usually elongate. Christensenia differs from other genera in having palmately branched fronds (pinnate in other genera), net venation, and circular rather than linear synangia. Gametophytes (the small plant generation bearing egg- and sperm-producing organs) are large (among ferns) and thick and resemble thallose liverworts.
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 10,000 highly qualified scientists and 45 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information