By Maureen Gilmer
DIY Network.)
Fern reproduction is so mysterious it remained wrapped in mystery and magic until the middle of the 19th century. The reason is that -- unlike all other plants -- ferns don't flower and therefore produce no seeds. This led the ancients to imbue ferns with special powers, especially the power of granting invisibility. They thought that a plant with invisible "seed" must be capable of rendering people or other things invisible as well.
These "invisible" seeds meant that you could not propagate ferns except by cuttings. Ignorance reigned until the advent of the microscope, which allowed botanists to see that fern dust carried on the backs of the leaves was actually millions of single celled spores.
While I learned in botany classes that ferns reproduce by spores, I never really understood what makes a spore so different from a seed. That is until I read A Natural History of Ferns by Robbin C. Moran (Timber Press $29.95).
Moran tells us that ferns could not be grown in quantity until the role of spores was finally documented. It proved that there are really two stages in a fern's life cycle. What you see as the green plant is actually the second phase, a stage in which the spore is sterile and bears no sex organs.
Only when a single cell spore, contained in those rusty brown clusters on the underside of a leaf, falls to the ground can the first phase of fern life cycle begins. A fallen spore grows into a prothalli, a heart shaped flat mass of flesh with root-like anchors to hold it against wind and water. On the surface of the prothalli are super tiny scale-like sex organs, both male and female. When water is present, sperm cells literally creep out of the scales and crawl across the prothalli to the cleft of another scale, which has at its base an egg cell.
At conception growth of the prothalli stops, ending the first reproductive phase of the life cycle. The prothalli will then produce differentiated roots, stems and leaves. Unlike all seed plants, the second-phase adult fern will never bear sex organs of its own. Ferns produce only more spores as they mature.
This illustrates the chief difference between seeds and spores. Seeds are created via sex organs on a mature plant. Spores actually become an intermediate form of plant that exists only for sex. According to Moran, the complete fern life cycle can range from just a month to as much as two to three years.
My revelation at finally discovering the odd sex life of spores is just one of many new discoveries in this book. The writing is such that even a beginner can come to understand the nuance of this great green family of plants that elude so many.
Primary sections also include more on the life cycle and other unusual means of reproduction unique to ferns. The section on classification helps you generally group major ferns and some other closely related plants. You'll also delve into the fascinating world of fern fossils from the Carponiferous and Mesozic Eras. At that time immense forests of ferns dominated the Earth long before true seed plants evolved.
The latter half of the book explores unique ways that specific fern genera have adapted to less than ideal conditions. There is great reading on the origins of ferns around the world and their relationship to geography. Finally you'll enjoy unique tales of ferns and humans with their age-old connections.
A Natural History of Ferns is not an encyclopedia or a systematic presentation of fern genera and species. It is a collection of engaging essays by Moran, curator of ferns at the New York Botanical Garden. He has certainly changed the way I look at this most ancient flower-free plant family.
(Maureen Gilmer is a horticulturist and host of Weekend Gardening on DIY-Do It Yourself Network. E-mail her at mo@moplants.com. For more information, visit : www.moplants.com or www.DIYNetwork.com. Distributed by Scripps Howard News Service.)
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