I. Introduction.

Ferns - generally shade loving plants of small size. Their upright leaves termed fronds are the most obvious portion of the plant. All forms in our region have an underground rhizome, with leaves and roots arising at the nodes. In the tropics, some species of ferns attain many feet in height, and indeed are tree-sized plants.

There is a distinct alternation of generations, and both generations are independent, photosynthetic plants.

II. Taxonomy - Class Filicinae, Order Filicales - chief order, with 11 families; other Fossil forms known.

III. Mature sporophyte.

A. Leaves or fronds are main portion - differ from angiosperm leaves in that:
1. there is an apical meristem so that the leaf continues to grow in length for some time, and
2. spores are often borne on the lower surface.
Most fronds are compound, although some are simple. The commonest form shows a stout central petiole, part of which forms the rachis from which arise the leaflets or pinnae.
B. The arrangement of the vascular tissue in ferns is highly variable, but distinct for each group. Stelar arrangements include:
1. Protostele - single vascular bundle in center, cortex around it.
2. Siphonostele - usually central pith surrounded by one or more rings of vascular tissue, alternating xylem & hloem.
3. Dictyostele - scattered groups of vascular tissue.

A. Vegetative - Occurs in two ways
1. Death of older portion of rhizome with separation of growing apices.
2. Formation of buds on leaves which then drop off and grow into new sporophytes - Rare.
B. Asexual reproduction
1. Sporophyte
    Spores borne in sporangia - usually on undersurface of the leaf. Not all leaves are fertile, and the fertile leaves may be very different from the vegetative forms. Actual distribution and form of sporangia is highly varied, and is a significant taxonomic feature. In some forms, the sporangia are scattered evenly over the leaf surface or they are gathered together into groups known as sori. The sori may grow along the veins of the leaf, or be associated with the margins of the leaf. Sori are frequently protected by an umbrella-like indusium. (There may be multiple indusia). Other sori, especially marginal sori are protected by a false indusium - the margin of the leaf curling over them.
The Sporangium is a thin-walled case almost encircled by a ring of thick-walled cells - the annulus. This aids in spore dissemination. Sporogenous tissue in the sporangium forms spore mother cells which meiotically form spores. Except for two small families of water forms, ferns are homosporous.
C. Gametophyte
    Gametophyte is known as a prothallus. It is a small heart-shaped green structure about size of thumbnail. The undersurface bears the rhizoids, antheridia and archegonia. They are homothallic. Archegonia are borne near the notch. The antheridia tend to be nearer the apex. Antheridia are formed first, and are small - consisting of only 3 or 4 sterile jacket cells surrounding 32 sperm.
    Archegonia are formed later, closer to the notch and are small, but of typical archegonial form.
Fertilization is dependent upon a water film.
The resulting embryo sporophyte has the usual foot, root, shoot and leaves.
 

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