Our Fine, Feathery Ferns: A Sight for Sori
by W. Carl Taylor
EDITOR'S NOTE: This article is reprinted from LORE magazine (vol. 44, no. 2, (June, 1994), p. 14-19), a benefit of museum membership. ©1996 Milwaukee Public Museum, Inc.
Recognizing Ferns
The word "fern" is from the old Anglo-Saxon "fearn" meaning feather. Like feathers, the leaves of most ferns are delicate and divided. We can imagine delicate, divided, "feathery" fern leaves in moist, shady woods. While this image fits many ferns, others look very different. Some have leathery, undivided leaves. Others may be as tiny as a moss or as large as a tree. In addition to the shady woods of our region, ferns are found in many places. Most ferns are tropical, often growing upon the trunks and branches of trees. A few ferns are aquatic. Some even occur in the desert tucked under rocks out of the heat of the sun. Although various kinds of ferns have different leaves, grow to different sizes, and are found in different places, nearly all can be recognized in two ways.
First, ferns can be recognized by their production of spores, tiny, one-celled reproductive bodies produced in small spore cases. These cases are clustered together into brownish spots called sori, which are often located on the lower sides of leaves.
Second, ferns can be recognized by the way their new leaves develop, unrolling from base to tip as they mature. These leaves resemble the head of a fiddle, the "fiddleheads" characteristic of most ferns.
Over 60 different kinds of ferns are native to Wisconsin. Most of our species can be distinguished from one another by the division of their leaves and the shape and location of their sori. For example, Walking Fern has undivided leaves with elongate sori whereas the Wood Fern has divided leaves with round sori.
Life History of Ferns
A fern may be visualized as a plant tipped over on its side with its stem laying on the ground. As the fern stem grows along the ground, it produces roots along its lower side and leaves along its upper side. The leaves bear spores in spore cases clustered into dark colored sori. Spores develop within each spore case through a process of successive cell divisions during which each cell's chromosome number is reduced from two sets to one set.
Upon maturing, spores are catapulted away by the rapid opening and closing of the spore case. When a spore lands in a suitable place it germinates to form a prothallus, usually green, heart-shaped, and less than one-quarter of an inch across. On the lower surface of the prothallus, special structures produce eggs and sperm. Eggs form at the bottom of bottle-shaped structures around the notch of the heart. Sperm form in spherical bodies nearer the pointed end of the heart. A drop of water on the prothallus at the right time enables sperm to swim across the heart to an egg and fertilize it. Fertilization combines the chromosome sets of sperm and egg and creates a new, tiny fern which begins to develop on the prothallus. As the fern grows to maturity, the prothallus withers away.
The life history of ferns determines where ferns will be found. Although it is not obvious, it is crucial to have a drop of water at the proper time and place to allow sperm to swim to an egg and complete the fern's life cycle. Lack of moisture limits the occurrence of ferns. This is why more ferns are found in moist, shady woods than in dry, sunny prairies. Moist, shady woods are more likely to have water drops present at the proper time and place to allow sperm to swim to eggs.
Growing Ferns
Growing ferns from spores is easy and allows you to observe parts of the fern life cycle not often seen in nature. For example, the prothallus is rarely noticed in a shaded woods because of its small size, but it is readily observed in spore cultures. Growing ferns from spores is also a good way to obtain ferns for a garden. To grow ferns from spores you will need ripe fern spores, a peat pot, and a clean jar with a lid.
Many species of Wisconsin ferns bear ripe spores in June and July. Remove the part of a fern leaf bearing sori with ripe spores. Dark colored spore cases within the sori are an indication of ripe spores inside. Place the sori-bearing leaf portion in a half-folded sheet of clean, smooth, white paper. Ripe spores will be released within a day. Remove the leaf, gently tap the paper on its fold and a dark colored powder of spores should be concentrated within the fold.
Peat pots, used for starting plants, are available from most garden shops. Saturate and sterilize the peat pot by pouring boiling water over it. Allow the peat pot to drain and cool slightly for a few minutes. Invert the jar and unscrew the lid. Lift the jar, place the warm, moist peat pot on the lid, and replace the jar loosely on its lid. When the peat pot cools to room temperature, lift the jar.
Dust the spores from the folded paper over the peat pot and return the jar loosely on its lid. Place the inverted jar near an east or north window out of direct sunlight. In a few weeks you will begin to see green, moss-like prothalli growing on the surface of the moist peat pot. Later tiny ferns will be seen growing from the prothalli. When the young ferns are an inch or more in size they can be transplanted.
You might consider establishing a fern garden if you have a shaded area in your yard. Many of our native ferns grow well under cultivation. Basically, you should try to simulate the natural habitat of the ferns you wish to grow. An area with partial shade, possibly on the north side of a building might be a good place to consider for growing ferns. They do best in rich, moist, but well drained soil. Native ferns which you might try in a garden include Wood Fern, Northern Maidenhair Fern, Ostrich Fern, Lady Fern, and Cinnamon Fern. Any of these ferns could be quite striking in a moist, partly shaded garden. Several other kinds of hardy ferns are also often available at nurseries.
Watch for our fine, feathery ferns on your hikes this summer. Grow some ferns from spores. Try several ferns in your garden. They are a sight for sori!